INSTITUT*NEELneel.cnrs.fr/IMG/pdf/Brochure_2016_2017.pdf · 5 INSTITUT NEEL Grenoble Proposition de...

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Directeurs adjoints

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MASTER 1

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INSTITUT NEEL Grenoble Proposition de stage Master 1 - Année universitaire 2016-2017

Table des matières / Contents Investigation of Second Harmonic Generation in Plasmonic Nanostructures ........................... 5 Mesure de fluctuations de vitesse par anémométrie à fibre optique .......................................... 6 Fluctuations hydrodynamique en conditions extrêmes .............................................................. 7 Turbulence Quantique : étude expérimentale ............................................................................. 8 Probing the superfluid density in high temperature iron superconductors ................................. 9 Etude de matériaux magnétiques à base d’élément de terre-rare et de cobalt ou fer ............... 10 Fluctuations of the Josephson current in a two-terminal Josephson junction at equilibrium...11 Systèmes Hybrides Spin-Nanorésonateurs mécaniques……………………………………...12

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Investigation of Second Harmonic Generation in Plasmonic Nanostructures

General Scope:

Nonlinear nanophotonics is a great opportunity for opening new and promising paths toward a wide range of practical applications in sensors, quantum computers, cryptography devices... The main challenge is to enhance non-linear response of nanosized particles in order to integrate them in optical components. We use metallic structures because they support localised surface plasmons (LSPs) – collective oscillations of free electrons. When excited with a laser tuned at the LSP resonance wavelength, these structures exhibit a great near field enhancement that strongly amplifies nonlinear processes.

Research topic and facilities available:

The main objective of this internship is to investigate SHG in plasmonic nanostructures. SHG is a nonlinear process in which two incident photons are converted into a single photon at the half wavelength. The student will perform nonlinear optical measurements. He/she will learn up-to-date techniques ranging from ultra sensitive measurements to femtosecond pulse manipulation and non-linear optical conversion. Meanwhile, he/she will run Finite Element Method simulations (with COMSOL) in order to compare experimental measurements with a numerical model that has been developed by our team. The nanoscale localization and enhancement of the electric field around the nanostructure, the origin of the SHG or the coupling between two plasmonic nanostructures are different aspects that can be addressed during the internship. This project will be part of a wider research program, lead by G. Bachelier, that has been granted by the ANR. Hence, all necessary means will be available. Collaborations and networking: M. Ethis de Corny and G. Laurent (PhD, NOF), G. Nogues (NPSC), G. Dantelle (OPTIMA). Required skills: An experimentalist profile is targeted here. Though, a theoretical background in electromagnetism, nonlinear optics and/or programming skills in MATLAB/COMSOL will be welcome. Starting date: As soon as possible. Contact: Name: Guillaume Bachelier Institut Néel - CNRS Phone: 04 56 38 71 46 e-mail: [email protected] More information: http://neel.cnrs.fr

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Mesure de fluctuations de vitesse par anémométrie à fibre optique

Cadre général : La physique de la turbulence est étudiée depuis plus d’un siècle mais elle demeure un sujet ouvert. Au sein d’un écoulement turbulent, des tourbillons de tailles différentes interagissent. L’étude de ces interactions entre structures et la compréhension des caractéristiques des très petites échelles constitue un défi majeur qui nécessite la miniaturisation des sondes de mesure. Les capteurs doivent être suffisamment petits pour résoudre les plus petites structures tout en étant robustes et sensibles. Dans cet esprit, nous avons entrepris à l’Institut Néel le développement d’un anémomètre à fibre optique. Les premiers essais ont montré que le principe de fonctionnement de la sonde est valide (voir Figure). Un nouveau prototype est en cours de réalisation. Afin de permettre l’exploitation de la sonde, il est maintenant important de caractériser sa réponse dans un écoulement.

Fig. [à gauche] L’écoulement arrive par la gauche et défléchit la membrane. Son déplacement est mesuré par la fibre optique (d’après Watson et al.) [à droite] Capteur commercial à fibre (FISO).

Sujet, moyens disponibles :

Nous souhaitons recruter un étudiant en stage afin d’adapter les moyens de tests de l’Institut à l’étude du comportement de la sonde. Pour cela, un écoulement d’air comprimé filtré sera utilisé pour produire un signal de turbulence connu. La sonde sera montée sur une tête goniométrique. L’étudiant devra monter le banc de test à partir de ces différents éléments et l’instrumenter. Il effectuera ensuite une étude systématique de la réponse dynamique de la sonde en fonction de l’angle d’incidence. Le traitement des données devra permettre de caractériser les performances de la sonde. De ce travail dépendra la nouvelle génération de ce type de capteur. Interactions et collaborations éventuelles : L’anémomètre est développé au sein d’une collaboration interne à l’Institut Néel, entre des hydrodynamiciens et des opticiens. L’étudiant sera amené a interagir pleinement avec les différents acteurs de la collaboration. Il devra également collaborer avec les équipes techniques du laboratoire pour les questions de mécanique.

Formation / Compétences : Compétences développées : Optique fibrée, Instrumentation, Hydrodynamique & Turbulence, Acquisition & Traitement du signal. Période envisagée pour le début du stage : indifférente Contact : Chabaud Benoit, Institut Néel – CNRS/UGA, [email protected] (contacts alternatifs : Philippe Roche, [email protected] , et Jochen Fick, [email protected] ) Site web : http://hydro.cnrs.me

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Fluctuations hydrodynamique en conditions extrêmes Cadre général : De tous les fluides, l’hélium cryogénique est celui présentant la plus faible viscosité. Cette propriété est mise à profit en laboratoire pour produire des états turbulents très intenses, inaccessibles aux expériences traditionnelles. L’enjeu consiste à tester les théories de la turbulence dans des conditions optimales. Les installations cryogéniques du CERN, uniques au monde par leur puissance réfrigérante, ont permis de construire une expérience de jet d’hélium gazeux de tous les records, en particulier en terme d’intensité turbulente (nombre de Reynolds jusqu’à 107). Après une première campagne de mesure ayant permis de valider l’expérience en Juillet 2015, les prochaines campagnes sont possibles jusqu’en 2017 grâce à un financement européen. Sujet, moyens disponibles :

Nous souhaitons recruter un étudiant qui participera aux futures campagnes. Concrètement, une partie du travail sera consacrée à l’instrumentation et à la mise en œuvre de l’expérience. L’autre partie sera consacrée à la validation des données, et en particulier aux tests des lois de turbulence à très haut nombre de Reynolds (statistique des fluctuations de vitesse et de température). L’activité est basée à Grenoble, avec des séjours courts et réguliers au CERN.

Interactions et collaborations éventuelles : L’expérience, coordonnée par notre laboratoire, est menée dans le cadre d’une collaboration inter-laboratoires et dans le prologement de la collaboration européenne EuHit (www.euhit.org). En particulier, le CERN héberge l’expérience principale mais des expériences de plus petites tailles seront mises en œuvre dans notre laboratoire.

Formation / Compétences : Compétences développées: Instrumentation & Mesures bas bruit, Hydrodynamique & Turbulence, Physique des basses températures & Cryogénie, Acquisition & Traitement du signal. Période envisagée pour le début du stage : indifférente. Durée minimum de 3 mois Contact : Roche Philippe, Institut Néel – CNRS/UGA [email protected] (04 76 88 11 52)

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Turbulence Quantique : étude expérimentale

Cadre général : En dessous de 2,17 K, l’hélium liquide acquiert des propriétés superfluides : il peut s’écouler sans viscosité et la vorticité de son champ de vitesse devient quantifiée. On s’attend donc à ce que sa turbulence, appelée « Turbulence Quantique », diffère de la turbulence « classique ».

D’après plusieurs études récentes, il semble que la principale différence soit concentrée au niveau des plus petits tourbillons présents dans ces 2 types de turbulence. En effet, en l’absence d’une dissipation efficace, on s’attend à ce que les tourbillons superfluides s’accumulent aux petites échelles de l’écoulement.

L’objectif est de détecter et comprendre cette différence, grâce à un détecteur conçu à cet effet.


Dans le cadre du stage et de la thèse, l’étudiant développera un capteur de vortex miniature (<100 µm) en tirant profit de l’environnement grenoblois en nano-technologies (nanofab, PTA/Minatec). Ce capteur sera ensuite exploité dans nos différents écoulements d’hélium liquide, soit superfluide soit classique, afin de comparer les propriétés physiques des deux types de turbulence. L’un de ces écoulements sera la soufflerie TOUPIE, spécialement construite pour répondre à cet objectif, et qui bien vient de bénéficier d’un upgrade pour atteindre des températures approchant 1K, un record pour une soufflerie cryogénique de grande taille.

Interactions et collaborations éventuelles : Le projet s’inscrit dans le cadre du projet inter-laboratoires (CEA/CNRS/ENSL/INP/UGA) SHREK (financement ANR), centré sur une cellule d’étude de la turbulence superfluide de très grande taille (env. 1m3). Des expériences seront aussi conçues pour cette cellule.

Formation / Compétences développés : Hydrodynamique & Turbulence quantique, Physique des basses températures & Cryogénie, Nanotechnologie & Technique de microfabrication, Acquisition & Traitement du signal, Instrumentation & Mesures bas bruit Période envisagée pour le début du stage : indifférente. Stage de 3 mois minimum Contact : Roche Philippe, Institut Néel – CNRS/UGA [email protected] (04 76 88 11 52) http://hydro.cnrs.me

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Tourbillons superfluides (simulation)

Tube de Pitot miniaturisé permettant la mesure de

fluctuations de vitesse superfluide

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Probing the superfluid density in high temperature iron superconductors

Cadre général : The mechanisms responsible for superconductivity are a central issue in contemporary physics. Very successful models have allowed a deep understanding of these mechanisms in pure compounds and many alloys. But the debate is completely open about the origin of superconductivity in materials with strong electronic correlations where the electron-electron interactions are no longer negligible. Among these systems the high temperature superconductors based on iron successfully grown recently, are very interesting from a fundamental point of view but also possibly for future applications. From a fundamental point of view, spin fluctuations, but also other kind of fluctuations (nematicity, orbital order ...) could intervene for the mechanisms of this novel superconductivity [1]. Consequently, in these systems, the link between the different electronic phases have to be clarified. The use of an external parameter such as pressure can allow us to tune the ground state and to approach the point where the fluctuations play an important role. Sujet exact, moyens disponibles :As FeSe (the elementary brick of this new superconductors) order magnetically under a pressure of 1GPa [2] we wwant to probe its superconducting properties in measuring the magnetic penetration depth λ and the coherence length ξ in proximity of this critical pressure. These lengths are very fundamental and directly related to the electron density forming the superfluid condensate but also to the superconducting gap [3]. Moreover, the temperature dependence reflects the existence of possible nodes in the superconducting gap, a consequences of broken symmetry induced in the superconducting state. Interactions et collaborations éventuelles : We will develop and use a new experimental set-up. The candidate will have the opportunity to interact with several collaborators at Neel institute and out the laboratory.

[1] Fernandez & al; Nature Physics 10, 97–104 (2014) What drives nematic order in iron -based superconductors? [2] Medvedev & al; Nature Materials 8, 630 - 633 (2009) Electronic and magnetic phase diagram of FeSe with superconductivity at 36.7 K under pressure [3] Rodiere P & al; Phys. Rev. B 85 (2012) 214506 Scaling of the physical properties in Ba(Fe,Ni)(2)As-2 single crystals: Evidence for quantum fluctuations Formation / Compétences : The candidate will have a strong background in solid state physics, electromagnetism and quantum mechanics. We are working with an home made instrumentation developed in the laboratory, with world-wide performances. The candidate has to be interrested by experimental development. Période envisagée pour le début du stage : Contact : Rodière Pierre Institut Néel - CNRS : 04 76 88 12 70 – [email protected] Plus d'informations sur : http://neel.cnrs.fr/spip.php?rubrique811

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Etude de matériaux magnétiques à base d’élément de terre-rare et de cobalt

ou fer Cadre général : Le sujet s'inscrit dans le cadre des recherches effectuées par une équipe travaillant sur les propriétés physiques et structurales de matériaux. Nous cherchons à améliorer les propriétés des matériaux actuels et aussi à élaborer de nouveaux composés dont il faut comprendre les propriétés fondamentales. Les matériaux de cette famille peuvent, selon leur composition et leurs propriétés, avoir des applications variées allant des aimants permanents utilisés dans l’électrotechnique, ou les détecteurs aux matériaux pour l’enregistrement de haute densité ou la microélectronique moderne dite de spin. Sujet exact, moyens disponibles : Ce stage comporte une partie d’élaboration de ces composés, mais aussi de caractérisation de leurs propriétés physiques. La diffraction des rayons X sera utilisée pour étudier la structure cristalline tandis que la microscopie électronique sera mise en œuvre pour analyser la composition chimique. Au-delà des propriétés structurales nous nous intéresserons plus particulièrement aux propriétés magnétiques de ces matériaux à savoir : aimantation, température d’ordre, type d’ordre magnétique retenu par le composé en fonction de l’élément de terre rare. Ce stage est essentiellement à caractère expérimental, il sera aussi l’occasion de manipuler divers concepts plus fondamentaux vus au cours de l’année. Les équipements nécessaires pour mener ces recherches à l’Institut Néel sont opérationnels tant au niveau de la synthèse que de la caractérisation des propriétés physiques. Formation / Compétences : Le profil est celui d’un(e) étudiant(e) de Master 1 ou d’Ecole d’Ingénieur intéressé(e) par la physique expérimentale, désireux (se) de compléter sa formation et d’approfondir ses connaissances scientifiques et techniques en cristallographie et magnétisme au travers d’un stage au sein d’une équipe de recherche. Période envisagée pour le début du stage : printemps-été 2017 Contact : Isnard Olivier Institut Néel - CNRS 04 76 88 11 46 mel [email protected] Plus d'informations sur : http://neel.cnrs.fr

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Fluctuations of the Josephson current in a two-terminal Josephson junction

at equilibrium

Introduction : In the Josephson effect, a nondissipative supercurrent flows through a phase-biased weak link between two superconductors. The Josephson effect is one of the most important building block of quantum nanoelectronic circuits, which are the subject of intense theoretical and experimental investigations. In our group, we study more specifically more complex Josephson junctions with three or four terminals, as shown in the figure. In general, the current is not flat in time. On the contrary it

fluctuates, for instance because of the granularity of the charge carriers, or because of a finite temperature. The general motivation for the internship is to calculate « generalized » quantum fluctuations of the current, which will pave the way towards a description of those junctions in terms of density matrix theory, used routinely in atomic physics. Thus, the goal is to initiate a research program intended to bridge between those three- or four-terminal Josephson junctions and atomic physics. Proposed work-program : The goal of the internship is to evaluate those generalized quantum fluctuations of the Josephson current, starting with a two-terminal Josephson junction in the absence of bias voltage. The method relies on analytical calculations in the framework of wave-function calculations, similar to those studied in the M1 course of Quantum Mechanics. It will be asked to the student to first calculate the Josephson current as a function of the phase difference, using the proposed wave-function appproach. Thermal fluctuations of the Josephson current will next be evaluated. The calculation of higher-order current fluctuations is also scheduled, intended to provide evidence for a current switching at random between two opposite values. Interactions and possible collaborations : This project is within the framework of national and international collaborations that we have been developping over the last years. It is expected that the student should interact on a daily basis with the other members of our group in Grenoble (Denis Feinberg and Serge Florens), as well as with our close collaborator Benoît Douçot in Jussieu. The student is expected to visit the experiment of François Lefloch in CEA-Grenoble. This work is also within an on-going collaboration with the experimental group of Moty Heiblum at the Weizmann Institute in Israël. Required skills : It is expected that the student should master well the ideas of his M1 course on Quantum Mechanics. Period for the internship : Anytime during academic year 2016-2017 Contact : Régis Mélin Institut Néel - CNRS 04-76-88-11-88, [email protected]

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Systèmes Hybrides Spin-Nanorésonateurs mécaniques

Le refroidissement et l’observation d’un oscillateur mécanique macroscopique dans son état quantique fondamental, réalisé en 2010-2011 dans plusieurs laboratoires, permet maintenant d’envisager la génération d’états mécaniques non-classiques. Pour ce faire une stratégie consiste à coupler ce résonateur mécanique ultrafroid à un autre système quantique, un qubit, dans le but de transférer sa nature quantique à l’oscillateur. Ce faisant on réalise un système hybride mécanique couplant les deux briques de bases de la mécanique quantique [1,2].

Le groupe de recherche Nano-optomécanique quantique hybride de l’Institut Néel explore une voie dans laquelle des nanofils de carbure de silicium sont couplés au spin électronique d’un centre coloré du diamant, le centre NV (pour Nitrogen-Vacancy). Une première expérience de principe [1] a permis de développer ce système hybride spin-oscillateur: un centre coloré hébergé dans un nanocrystal de 50 nm de diamètre a été déposé à l’extrémité d’un nanofil de SiC. En immergeant le système dans un très fort gradient de champ magnétique, par effet Zeeman le spin du centre coloré est couplé à la position de l’oscillateur. On a pu ainsi montrer que les vibrations de l’oscillateur sont encodées sur le spin électronique. Ce projet vise à explorer de nouveaux mécanismes de couplage dans ces systèmes hybrides et à étudier le couplage spin-oscillateur en sens inverse, c'est-à-dire d’encoder l’état du spin électronique sur la position de l’oscillateur, reproduisant ainsi l’expérience de Stern et Gerlach avec des objets macroscopiques.

Pour ce faire, une sensibilité en force extrême est requise car la force exercée par le spin sur l’oscillateur est de l’ordre de ~20 aN pour un gradient de 1e6 T/m. De tels niveaux de sensibilité sont accessibles avec des oscillateurs mécaniques de très faible masse, comme démontré à température ambiante sur les nanofils de SiC [2]. De même, il est nécessaire de lire avec une grande précision les vibrations de ces nanofils. Les travaux en cours au laboratoire démontrent que la lecture optique des vibrations de nanofils permet de résoudre avec une grande dynamique leur mouvement Brownien. Enfin des protocoles avancés de manipulation du spin électronique ont également été mis en œuvre [3] au laboratoire qui ont permis de mettre en évidence la synchronisation du spin sur la vibration mécanique [5]. On a ainsi pu observer l’analogue phononique du triplet de Mollow en électrodynamique quantique, apparaissant lorsque le qubit de spin est fortement excité par les vibrations du nanofil. [1] O. Arcizet et al, Nature Physics 7, 879 (2011). [2] A. Gloppe et al, Nature Nanotechnology (2014). [3]S. Rohr et al., PRL 112, 010502 (2014) [4] B. Pigeau et al, Nature Communications ( 2015). [5] L. Mercier de Lépinay et al., arXiv:1503.03200 (2015). Interactions et collaborations: NEEL, ENS Cachan, labo. Kastler Brossel, Uni-Basel. Formation / Compétences : Ce sujet permettra d’acquérir un savoir-faire en nano-optique, en nanosciences et en manipulation de système quantiques. Même si ce projet revêt un fort caractère expérimental, l’aspect novateur des systèmes hybrides nanomécaniques requiert un intérêt poussé pour la formalisation théorique. Contact : Arcizet Olivier- Benjamin Pigeau, Institut Néel - CNRS : 04 76 88 12 [email protected]. Plus d'informations sur : http://neel.cnrs.fr

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MASTER 2

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Table des matières / Contents Full Quantum interference experiments using single electron charge pulses .......................... 17 Coherent mechanical driving of the spin of an individual magnetic atom with surface acoustic waves ........................................................................................................................................ 18 Triplet photon generation in optical non linear waveguides .................................................... 19 Ultra-cold Nanomechanics ....................................................................................................... 20 Synthesis of luminescent garnet nanoparticles for white LEDs ............................................... 21 Deciphering the folding of DNA origami ................................................................................ 22 Electrodynamics of Disordered Superconductors investigated by and for Kinetic Inductance Detectors (KIDs). ..................................................................................................................... 23 Recherche de la supraconductivité dans des bi-couches de graphène sous haute pression ..... 24 Étude de la compétition sous haute pression entre les ordres de charge et la supraconductivité dans les cuprates de mercure à haute température critique ...................................................... 25 Highly sensitive scanning probes for nanoscale thermal microscopy ...................................... 26 Visualize Unconventional Superconductivity .......................................................................... 27 Exploring Antiskyrmions ......................................................................................................... 28 Magnetic multilayers for coupled domain walls and skyrmions .............................................. 29 New generation of phosphors for LED lighting prepared by sol-gel method .......................... 30 Fluctuations hydrodynamique en conditions extrêmes ............................................................ 31 A single spin transistor for quantum processing ...................................................................... 32 Epitaxial Superconducting Quantum NanoWires .................................................................... 33 Graphene based superconducting quantum bit ......................................................................... 34 Competing electronic orders in the two-dimensional limit ...................................................... 35 Large scale spin-based quantum information processing in Si28 based semiconductors ........ 36 Suspended graphene and nanotubes for low temperature opto-electronics. ............................ 37 Three-dimensional experimental study of a quantum fluid: What is the dynamic of the quantum vortex? ....................................................................................................................... 38 Recherche de nouveaux supraconducteurs à haute température critique ................................. 39 Study of the physical properties of new unconventional superconductors under extreme conditions of pressure ............................................................................................................... 40 Glass Nanomechanical Resonators in the Quantum Ground State .......................................... 41 Fibered Nano-Optics Tweezers for Biological Applications ................................................... 42 Optical trapping for biological applications ............................................................................. 43 Evaporation in a nanoporous material: from local to collective .............................................. 44 Novel magnetic phases in frustrated fluoride compounds ....................................................... 45

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Coherent quantum phase-slips in Josephson junction chains measured in a quantum bit ....... 46 Charge detection by electrostatic force microscopy in quantum devices ................................ 47 Scanning gate microscopy on graphene quantum point contacts ............................................. 48 Résolution de nouvelles structures cristallines par Movie-Tomography en Diffraction Electronique ............................................................................................................................. 49 Quantum Hall interferometry in high mobility Graphene ........................................................ 50 Visualizing quantum Hall edge channels in Graphene ............................................................ 51 Bio-Activation of Mesoporous Silica Nanoparticles by selective DNA destructuration ......... 52 Confined nucleation and growth of molecular nanocrystals for biophotonics and advanced solid-state NMR ....................................................................................................................... 53 E-beam electromechanics for quantum nanomechanical engineering ..................................... 54 Electroless deposition of magnetic nanotubes and core-shell nanowires for a 3D spintronics 55 Quantum superpositions of causal relations ............................................................................. 56 New generation of phosphors for eco-efficient LED lighting: Pechini method ...................... 57 Mesure de fluctuations de vitesse par anémométrie à fibre optique ........................................ 58 Growth conditions to stabilize polar faces of ferroelectric crystals ......................................... 59 Growth of the chiral ferromagnet LiFe5O8 by high temperature flux method ........................ 60 Turbulence Quantique : étude expérimentale ........................................................................... 61 Dielectric properties of the Cooper-pair insulator .................................................................... 62 Synthesis of Chiral Crystals for magnetism, spintronic and Nonlinear Optics ........................ 63 Quantum simulation in circuit-QED ........................................................................................ 64 Nouveaux matériaux magnétiques fonctionnels ...................................................................... 65 Investigation of magnetization processes in R-M intermetallic compounds ........................... 66 Development of new magnetic actuators for biology applications at the cellular scale .......... 67 Growth of ferrimagnetic spinels for spin-filtering ................................................................... 68 Scanning Josephson Tunneling Microscopy: visualizing bound states in Superconductors ... 69 Model hard-soft magnetic nanocomposites .............................................................................. 70 Plasmonic response of copper nanoparticles during their growth on TiO2 ............................. 71 Mixed order phase transition .................................................................................................... 72 Listening to the noise of a four-terminal Josephson junction .................................................. 73 Systèmes Hybrides Spin-Nanorésonateurs mécaniques ........................................................... 74 Electric field manipulation of skyrmions……………………………………………………..75 Non-equilibrium quantum modeling of nano-structure based solar cells ………………...….76

INSTITUT NEEL Grenoble

Proposition de stage Master 2 - Année universitaire 2016-2017

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Full Quantum interference experiments using single electron charge pulses Context : Interference experiments are at the heart of quantum mechanics and have lead to immense achievements over the last two decades, in particular in the field of quantum optics. Due to the tremendous progress in nanofabrication techniques, it is now possible to isolate and manipulate coherently single electrons, which opens the way to perform quantum optics like experiments with electrons. Due to the fact that electrons in solids are strongly interacting particles, new quantum entanglement schemes can be envisioned, not possible with photons. References: Hermelin et al., Nature 477, 435-438 (2011); Yamamoto et al., Nature Nanotechnology 7, 247-251 (2012), Dubois et al. Nature 502, 659–663 (2013); Takada et al. PRL. 113, 126601 (2014)

Fig. 1. SEM image of an Aharonov-Bohm interferometer defined in a two-dimensional electron gas. The single electrons are injected by short voltage pulses (on the left) and single shot detected with a single charge detectors at the outputs (on the right). Objectives: The main objective of this proposal is the unprecedented realization of a full quantum interference experiment by manipulating and detecting electrons in a quantum conductor at the single electron level. Full quantum operation will bring the recent field of electron quantum optics at a level of its photonic counterpart and will be a major step in the field of Mesoscopic Quantum Physics with possible applications to quantum information. To realize such a full quantum experiment, we will combine our recently developed quantum interferometer with single electron sources and single electron detectors, presently developed within the research consortium. Possible collaboration and networking : This project is realized within a funded ANR research collaboration between the nanoelectronics group, CEA Saclay and the theory group of CEA Grenoble. M2 Internship susceptible to be pursued towards a PhD degree: yes (funding available) Education / Competences: Project for Master level & Engineering degree; we are looking for a motivated student who is interested in experiments that are challenging from the experimental as well as theoretical point of view. Possible period for the internship: up to 6 months in early 2016 Contact: Christopher BAUERLE & Tristan MEUNIER Institut Néel - CNRS: 047688 7843 e-mail: [email protected], [email protected] For more information: http://neel.cnrs.fr



18

Coherent mechanical driving of the spin of an individual magnetic atom

with surface acoustic waves

Context: Individual spins in semiconductor nano-structures are promising for the development of quantum information technologies. Spin based quantum systems typically rely on resonant magnetic field to drive coherent transitions between different spin states. Although such magnetic driving has been effective, developing alternative modes of control opens new routes for coupling disparate quantum states to form an hybrid quantum system. Particularly useful examples are electric fields, optical fields and mechanical lattice vibrations. The last of these represents direct spin-phonon coupling which garner fundamental interest as a potential mediator of long-range interaction between remote solid state spin qubits. Detailed project and means available: Thanks to their expected long coherence time, localized spins on individual magnetic atoms in a semiconductor host are an interesting media for storing quantum information. The spin of an individual magnetic atom inserted in a semiconductor quantum dot (QD) can be probed and initialized optically. Neel Institute has a long lasting experience in the control of individual magnetic atom in semiconductors. We recently demonstrated that the spin of an individual chromium atom (Cr) inserted in a QD can be used as an optically addressable qubit with large intrinsic spin to strain coupling. In this work, we will exploit the intrinsic spin to strain coupling of Cr to perform coherent mechanical driving of the spin of the magnetic atom. Controlled dynamical strain will be applied on Cr-doped QDs using surface acoustic waves (SAW). SAW, phonon-like excitations bound to the surface of a solid, are widely used in modern electronic devices but are also proposed as efficient quantum bus enabling long-range coupling of a wide range of qubits. During this internship, we will develop SAW based devices on Cr-doped QD samples. Inter-digitated piezo-electric transducer working in the GHz range will be designed, realized and tested. Optical measurements and comparison with a developed model will permit to estimate the amplitude of the oscillating strain applied on individual QDs. The next step will be to combine SAW excitation with existing resonant optical pumping technique to probe the influence of pulsed oscillating strain on the Cr coherent dynamics. Controlling the area of strain pulses, we will perform Rabi oscillations on the {+1;-1} Cr spin qubit (see figure). Sequences of two π/2 pulses could be used for Ramsey types experiments for a mechanical determination of the coherence of the {+1;-1} qubit. Our system should allow to study a single spin in the sought-after "strong driving" regime (ΩRabi>ωqubit) and thereby shed new light on this exciting, but still under-explored area of quantum physics. Collaboration and networking: This work, mainly experimental, will be realized in the framework of the CEA-CNRS group «NanoPhysique et Semi-Conducteurs» (CNRS / Institut Néel & CEA / INAC). The student will work in interaction with people in charge of the growth of samples at the University of Tsukuba and at INAC and will have access to technology platforms (Nanofab, PTA). He/she will be also involved in the modeling of the spin dynamics in the studied nano-structures. This internship can be followed by a PhD thesis on the same topic. Required profile: Master 2 (or engineering degree) with good knowledge in solid state physics (electrical, optical and mechanical properties), quantum mechanics, optics, electronics. Foreseen start for the internship: March 2017 Contact : Lucien BESOMBES, Institut Néel ; 04 56 38 71 58 ; lucien.besombes@grenoble .cnrs.fr



19

Triplet photon generation in optical non linear waveguides

Cadre général : This position concerns Triple Photons Generation (TPG). It is based on a third order nonlinear optical interaction is the most direct way to produce pure quantum states of light, called three-photons states.

These states exhibit three-body quantum entanglement and their statistics go beyond the usual Gaussian statistics relevant to coherent sources and optical parametric twin-photon generators, offering thus outstanding potential applications in the field of quantum information. Undoubtedly, three-photons states are new quantum tools to study the non-intuitive properties of quantum mechanics. In 2004, we made the first experimental demonstration of a pure TPG [Opt. Lett. 29, 2794-2796 (2004)], which means that the three photons were created from a single one, using a two-wave stimulation scheme in a phase-matched KTiOPO4 (KTP) bulk crystal. This pioneer work has opened new exciting opportunities in quantum optics. We made the classical and quantum theory of TPG [J. Opt. Soc. Am. B 25(1), 98 – 102 (2008) ; Phys. Rev. A, 85(4) 02389 1-12 (2012); invited conference at IEEE IPC San Diego 15 October 2014]. Sujet exact, moyens disponibles : TPG was first performed in a bulk crystal, which was possible only by stimulated the process using two modes of the field. We have then proposed a novel approach for spontaneous TPG in a guided configuration based on a conventional glass fiber [Opt. Lett. 26(15), 3000-3002 (2011) ; Opt. Lett., 40(6), 982 (2015) ; invited conference at Non Linear Optics, Hawaii, 27 July 2015]. TPG can benefit from both strong confinement and long interaction length. This result is very important since it indicates that an optical waveguide can enable to achieve a spontaneous TPG, which is completely impossible using a bulk medium. However, because the phase matching is only possible in an optical fiber between two different modes of propagation with a poor spatial overlap, the efficiency of TPG is expected to be very poor (about one triplet/s in a 10 meters long fiber) The work that is proposed in the framework of this internship is to combine the benefit of the high non linearity of bulk crystals such as KTP and the long interaction length and the strong confinement of an optical waveguide [Opt. Exp., 24(9), 9932(2016)]. It will be based on a ridge waveguide cut in a KTP bulk crystal (typically, a section of 10x10 µm2 and a length of two centimeters). Prior to stimulated TPG experiments in such a waveguide, a Third Harmonic Generation characterization has to be performed in order to test the injection and confinement efficiency. Interactions et collaborations éventuelles : Collaboration with : FemtoST (Besançon), Laboratoire de Physique et Nanostructures (Marcoussis), GAP (Université de Genève). Ce stage pourra se poursuivre par une thèse (ou ce sujet est limité à un stage M2...).PhD Possible Formation / Compétences :A background in laser optics, non-linear optics, quantum mechanics or quantum optics will be useful for the purpose of the project. Période envisagée pour le début du stage : starting from february or march 2016 Contact : B. Boulanger ([email protected]), V. Boutou ([email protected]) Institut Néel - CNRS : tél : 0476887807 / 0476887410 - Plus d'informations sur : http://neel.cnrs.fr



20

Ultra-cold Nanomechanics

Context : Keywords : quantum mechanics, nano-mechanics, non-linear phenomena, low temperatures, ground-state cooling Highly motivated students are sought for an ERC-funded project devoted to fundamental research using nanomechanics cooled down to the lowest possible temperatures. It has two facets: a macroscopic approach concerned with the quantum mechanics behavior of the moving device itself, and a microscopic one concerned with elementary excitations in quantum matter. Objectives and means available: The project is based on the « brute force » cooling of nanomechanical devices down to temperatures around/below 1 mK. For beams resonating around 100 MHz in their first flexure, the collective modes describing the motion are in their quantum ground states. Experiments probing mechanical quantum coherence are then possible, on a system which is at equilibrium. These coherence properties are linked to fundamental aspects of quantum theory, with new developments (e.g. stochastic collapse) and old paradoxes (e.g. Schrödinger cat). Properties of quantum matter are probed by looking at intrinsic mechanical dissipation mechanisms in the constitutive solids, or by immersing the devices in a quantum fluid: superfluid 3He. Intriguing states of matter can then be probed, with e.g. the Tunneling Two-Level Systems of glasses and the elementary excitations of the BCS superfluid. These experiments rely on cryogenic capabilities of the group: dilution cryostats and nuclear demagnetization cooling down to the 100 µK range. A new and unique platform allying microkelvin temperatures and microwave signals is being built in our group. Figures: a silicon-nitride high-quality nanomechanical beam coupled to a gate electrode (center), and a microwave cavity setup for quantum-limited readout of the dynamics (right). Possible collaboration and networking: This research is carried out at Institut Néel, in collaboration with other researchers from the laboratory. It is performed in the framework of the European Microkelvin Platform (EMP), with contacts to other ultra-low temperature facilities in Europe (UK, Germany, Finland…). Required profile: The student should have a strong interest in fundamental research and making challenging measurements at very low temperatures, as well as a thorough understanding of quantum theory at the Master’s Degree level. Ce stage pourra se poursuivre par une thèse financée Période envisagée pour le début du stage : Flexible Contact : Collin Eddy Institut Néel - CNRS : 04 76 88 78 31 [email protected] Plus d'informations sur : http://neel.cnrs.fr/spip.php?rubrique69&lang=fr



21

Synthesis of luminescent garnet nanoparticles for white LEDs

General Scope : White LEDs are part of the new generation of lighting devices, presenting the advantages to be more efficient in terms of energy conversion and more environmentally-friendly. They are prepared by combining a blue-emitting GaN-diode with inorganic materials, called phosphors, emitting in the yellow and/or red range (Figure 1a). The most commonly-used phosphors are some Y3Al5O12 crystals doped with Ce3+ as they present a high luminescence quantum yield (over 80%). However, due to their micrometer size, they induce scattering within the device and are responsible for light losses. In this context, the goal of this project is to reduce the dimension of the Y3Al5O12 crystals (Figure 1b) while preserving their high luminescence performances.

Figure 1: (a) Schematic of a white LED based on the combination of a blue LED and yellow phosphors. (b) TEM image of Y3Al5O12 nano-crystals. Research topic and facilities available: During this internship, we will use the solvothermal method at high pressure to prepare Y3Al5O12 and other garnet-type nano-crystals. The goal is to control the size of the particles (between 50 and 100 nm), as well as their crystallinity and their optical properties. This internship implies the material synthesis, their structural characterization (by x-ray diffraction, electron microscopy, dynamic light scattering) and their optical characterization (optical spectroscopy). All the equipment is available in the laboratory. Possible collaboration and networking: Interactions with the various members of the OPTIMA team at the Institut Néel Possible collaboration with the Institut Lumière Matière (Lyon) for more advanced spectroscopy Possible extension as a PhD: Yes, if funding. Required skills: Good skills in materials science are required. Starting date: February 2017 Contact: Name : Géraldine Dantelle Institut Néel - CNRS e-mail: [email protected] More information : http://neel.cnrs.fr

Blue LED λém=450 nm

80 nm

Micron-‐sized phosphors emitting at λém ~ 550 nm

(a) (b)



22

Deciphering the folding of DNA origami

General Scope : DNA nanotechnology benefits from the progresses in DNA synthesis and sequencing that permit to use DNA as a programmable material to self-assemble algorithmically nano-objects. Our research targets the development of molecular nanorobots that could measure and process information in biological environment. DNA origami pictured in Figure 1 is a class of DNA nanostructures that form programmable shapes with sizes of the order of few 100 nm. Although the process is very robust we lack the understanding of the folding process itself. Such understanding is crucial to foster the applications of the methodology toward interesting applications that are foreseen in physics and medicine.

Figure 1 AFM rendering of a DNA smiley obtained by

annealing a mix a short oligo and a large genomic DNA. The folding process still needs to be elucidated.

© Paul Rothmunds and Nick Papadakis

Figure 2 : nanocalorimetry results indicating the stable intermediates in the folding pathway of a DNA tetraedron

Research topic and facilities available: The internship proposes to study the folding pathway of model DNA nanostructures that are composed of few synthetic strands in order to decipher the folding intermediates. One concrete of the internship goal is to evaluate the cooperativity of the self-assembly. The student will perform nanocalorimetric experiments, represented in Figure 2, that can identify the presence of stable intermediates in the folding. The student will develop also the models that can first interpret the experimental data and second explain the folding process. The internship combines experimental and modelling work. Possible collaboration and networking: Collaborations include groups in Bordeaux, Paris, Oxford and Tokyo. Possible extension as a PhD: For excellent students, an extension as a PhD is possible. Required skills: The student must be highly motivated by experimental work or have good programming skills. Knowledge in biology and DNA nanotechnology is a plus but not mandatory. Starting date: March 2017 or earlier. Contact: Name: GUILLOU Hervé Institut Néel - CNRS e-mail: [email protected] More information: http://neel.cnrs.fr



23

Electrodynamics of Disordered Superconductors

investigated by and for Kinetic Inductance Detectors (KIDs) General Scope : Kinetic Inductance Detectors (KIDs) are RLC resonators made out of superconducting materials. They are state-of-the-art detectors for millimeter wave observations in astrophysics. The detection principle is based on the monitoring of the resonator frequency variation ω0=(LC)-1/2. When used as a photon detector the incident radiation breaks down Cooper pairs, modifying the kinetic inductance L and thus the resonance frequency. The superconducting gap △ sets in the photon detector cutoff frequency to hν>2△. In principle, within the classic BCS-superconducting theory Tc and △ are not independent parameters as △~1.76-2 KBTc. Thus, lowering the cutoff frequency requires to lower the working temperature T<< Tc. In this project we aim to develop a novel disruptive technology for light detection that are the SKID : Sub-gap Kinetic Inductance Detectors. These detectors are sensitive to photons with an energy hν laying well below twice the superconducting gap 2△. These detectors are innovative as they remove the operating temperature constraint when lowering the photon detection cutoff frequency. Low superfluid density material obtained in disorder superconductors is a key ingredient for the development of those new detectors. Research topic and facilities available : NbSi-material will be investigated. Amorphous NbSi is a highly disordered superconductor. Its normal state sheet resistance and its superconducting critical temperature Tc can be adjusted by varying the Nb content. The student will ensure all the steps of the study from the fabrication up to the measurements. She/he will design and nano-lithography the detectors. Test of the detectors will be realized in an optical dilution fridge refrigerator at 100 mK.

Possible collaboration and networking: The project is part of the ANR ELODIS in collaboration with two others laboratory : SPSMS from CEA Grenoble and CSNSM in Paris. Possible extension as a PhD: yes Required skills: Solid state physic knowledge, taste for experimental manipulation and strong motivation. Starting date: March or April 2017 Contact : Institut Néel - CNRS : Florence Lévy-Bertrand, 04 76 88 12 14, [email protected] Alessandro Monfardini, 04 76 88 10 52, [email protected]

Photo of a Kinetic Inductance Detector. Grey: silicon substrate. White: superconducting material. The resonator consists of a second order Hilbert shape fractal inductor and an interdigital capacitor. The resonator is capacitively coupled to the transmission line : top straight line.



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More information: http://neel.cnrs.fr

Recherche de la supraconductivité dans des bi-couches de graphène sous haute pression

Cadre général : La multiplication des études sur le graphène a ouvert la voie vers un grand nombre des nouvelles applications. Cependant très peu d'études expérimentales ont été réalisés sur ses propriétés électroniques lorsque il est placé sous haute pression. Il est vrai que étant extrêmement dur dans le plan basal, peu des changements sont attendus sur le graphène monocouche. Mais la physique des bi-couches sous pression risque d'être très riche. La liaison Van-der-Waals entre deux couches de graphène est très faible et doit être très sensible à la mise en pression. Un empilement symétrique du type A-A forcera une liaison inter-couches entre atomes de carbones. La bi-couche de carbone sera déformée vers une symétrie sp3, du type diamant ou silicène. Or des calculs théoriques récents [F. Liu et al., Phys.Rev. Lett. 111(2013)066804] prédissent une supraconductivité chirale dans des bi-couches de silicène, ainsi que d'autres propriétés supraconductrices anormales. La transformation sous pression vers une bi-couche "frippé" de type silicène risque d'être permanente et irréversible, conduissant à des réelles possibilités des nouvelles applications Sujet exact, moyens disponibles : Le sujet du stage consistera dans une première étape dans la fabrication de bi-couches de graphène, déjà mise au point dans l'Equipe HYBRIDE par V. Bouchiat, et leur adaptation pour son montage dans les cellules d'haute pression (déjà testée). Ensuite se feront des mesures de transport en fonction de la température jusqu'à 1K dans des cellules de pression pouvant atteindre les 30GPa avec M. Nunez-Regueiro de l'Equipe MagSup, d'une grande expérience dans l'étude des composés carbonés et supraconducteurs sous pression. Interactions et collaborations éventuelles : L'étudiant(e) sera amené(e) à collaborer avec des collègues des différentes équipes de l'IN. Ce stage pourra se poursuivre par une thèse. Formation / Compétences : Une bonne connaissance de la physique de la matière condensée est souhaitée. Période envisagée pour le début du stage : Contact : Nom Prénom Nunez-Regueiro, Manuel ; [email protected] ; tél.: 0476887838 Bouchiat, Vincent ; [email protected] ; tél.: 0476881020 Institut Néel - CNRS



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Plus d'informations sur : http://neel.cnrs.fr

Étude de la compétition sous haute pression entre les ordres de charge et la

supraconductivité dans les cuprates de mercure à haute température critique

Cadre général : L'origine de la interaction responsable de la supraconductivité à haute température critique (SHTC) continue à être un sujet extrêmement controversé. Depuis quelques années l'on a observé dans la plupart les familles de cuprates SHTC l'existence des ordres de charge (OC) en compétition avec la supraconductivité. Ils ont été observés dans la région sous-dopée du diagramme de phase des cuprates SHTC en coïncidence avec le, encore incompris, pseudo-gap. Ce fait semblait suggérer que leur étude pourrait apporter une nouvelle clé pour la compréhension du problème. En particulier, il est question de déterminer si ces ordres de OC sont intrinsèques a la physique des SHTC. Tout récemment nous nous sommes attaqués à l'étude des nouveaux monocristaux de haute qualité de cuprates de mercure, ceux même dont le record de température critique, Tc=166K à 26GPa, a été signalé par notre laboratoire (EPL72[2005]458). Étonnement, nous avons observé le OC sous une pression de 10GPa dans la région sur-dopée du diagramme de phase (voir figure; soumis Science). Dans cette région, le matériau est un liquide de Fermi normal et aucune propriété exceptionnelle, pouvant être reliée à la physique anomale des SHTC, n'est attendue. Ceci met en question l'hypothèse de l'importance du OC pour les SHTC. Cependant, il faut faire une étude complète des cristaux avec différents taux de dopage pour cerner clairement le comportement de ces matériaux sous haute pression. Cette étude est le sujet de ce stage pouvant être continué en thèse. Sujet exact, moyens disponibles : Le candidat fera des mesures de résistance électrique sous haute pression en fonction de la température pour déterminer l'évolution des propriétés de transport et de la supraconductivité dans de monocristaux de cuprates de mercure Hg-1201 avec différents taux de dopage (en collaboration avec Dorothée Colson, Service de Physique de l'État Condensé DSM/IRAMIS/SPEC, CEA Saclay). De cette manière il pourra observer comment la concentration de porteurs affecte l'apparition du OC sous pression. Il participera à des mesures de diffraction par rayons X réalisées à l'ESRF sous les mêmes monocristaux en collaboration avec G. Garbarino. La corrélation entre le deux types de mesure aidera à déceler si le OC est en effet une propriété du pseudo-gap et essentielle a la SHTC, ou un phénomène indépendant du mécanisme de la SHTC. Interactions et collaborations éventuelles : L'étudiant(e) sera amené(e) à collaborer avec des collègues du laboratoire de fabrication des échantillons, ainsi qu'avec les responsables de la ligne haute pression de l'ESRF dans le cadre des expériences de diffraction X. Ce stage pourra se poursuivre par une thèse. Formation / Compétences : Une bonne connaissance de la physique de la matière condensée est souhaitée. Période envisagée pour le début du stage : Contact : Nunez-Regueiro, Manuel ; [email protected] ; tél.: 0476887838 Institut Néel - CNRS Plus d'informations sur : http://neel.cnrs.fr



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Highly sensitive scanning probes for nanoscale thermal microscopy

Cadre général : With the advancement of the understanding of heat transfer at the nanoscale, there is currently a growing need for new experimental tools of high sensitivity to probe temperature and thermal conductivity at low dimensions. In this respect, new instruments have to be developed to fill that requirements. The Scanning Thermal Microscope (SThM) is one of them. This instrument consists of using an AFM environment and a probe equipped with a highly sensitive thermometer based on NbN developed at Néel. Using cutting edge nanotechnology processes coupled to thermal measures, our group at Néel has acquired a unique international expertise in this direction. On a more long term, this work will allow for the first time to extend the SThM technique to low and very low temperature experiments. Sujet exact, moyens disponibles : This internship aims at (i) developing a new resistive SThM probe for nanoscale quantitative thermal measurements, (ii) demonstrating the capabilities of the new technique on application-oriented to micro and nanostructured materials and systems, (iii) set this new instrument for thermal characterization at the nanoscale in an AFM environment. The major objectives of the project is to develop complementary expertise in SThM: resistive nanothermometry, local probe instrumentation, metrology and micro and nanofabrication. The outputs expected of the internship and then the thesis are the successful development of this new instrument: a highly sensitive SThM working from room temperature to very low temperature (dilution fridge); demonstration on specimens that will be developed within the ANR consortium (especially CETHIL and IEMN) are planned.

Fig. 1 First try of fabrication of a SThM probe from an AFM tip. The resistive thermometer has four contacts necessary for low noise measurements. The thermometer is only 100 nm large; it can be seen in the right panel. (Institut Néel, G. Julié, J.F. Motte) Interactions et collaborations éventuelles : this internship is a part of the ANR TIPTOP project, a 4 year R&D collaborative project with CETHIL INSA (Lyon), IEMN (Lille), and a SME CSI (Paris). Ce stage pourra se poursuivre par une thèse (ou ce sujet est limité à un stage M2...). Yes, the ANR project is financing a thesis scholarship from october 2017. Formation / Compétences: the candidate has to be motivated by the development of a new highly sensitive scientific instrument along with clean room work and innovative thermal measurements. Période envisagée pour le début du stage : february/march 2017 Contact : Olivier BOURGEOIS Institut Néel - CNRS : tél 334 76 88 12 17, 336 88 71 51 86 mel : [email protected] Plus d'informations sur : http://neel.cnrs.fr



27

Visualize Unconventional Superconductivity

General Scope Search for manifestations of new quantum effects in unconventional superconductors by means of a unique scanning microscope, by imaging the distribution of very small amounts of magnetic flux, typically a hundredth of the quantized flux (h/2e) carried by a vortex in a superconductor. Research topic and facilities available: Uranium based superconductors have unique properties as the extended 5f orbitals of U induce magnetic correlations in the electronic conduction band of these materials. UPt3 is the most prominent compound among these, the two step superconducting transition (Tc1= 0.55 K and Tc2= 0.49 K), discovered 25 years ago in Grenoble1, makes it the unique pendant known in solid state physics of superfluid 3He. The unique superconducting state of UPt3 is described by a complex two component order giving rise to three superconducting phases in the magnetic field, temperature (B,T) phase space. The low temperature, low field phase is expected to break time reversal symmetry. In consequence an increased vortex pinning is predicted1 at the domain boundary between domains of different chirality, see Figure 1

Fig. 3.) Domain walls (arrows) in superconductig UPt3 revealed by pinning of vortices, visualized by nanoSQUID microscopy.

Fig. 4.) NanoSQUID structured on a Si tip (coll. IRAM/ NEEL/LPN).

During the labwork the student will systematically image vortices above the surface of high quality single crystals of UPt3 in varying temperature, magnetic field amplitude and direction by means of our nanoSQUID microscope operating in a dedicated dilution refrigerator. ----------------------------------- 1Critical point in the superconducting phase diagram of UPt3 Hasselbach K et al.J, PRL. 1989 63 93-6. 2Vortex pinning and stability in the low field, superconducting phases of UPt3, Shung E. ; Rosenbaum T. F. ; Sigrist M. PRL. 1998 80 1078 Possible collaboration and networking: The project is carried out in the framework of a longstanding collaboration with colleagues of Néel CNRS and INAC CEA Grenoble in contact with other national and international groups. Possible extension as a PhD: Magnetism of superconductors Required skills: Experimental Physics, superconductivity, curiosity Starting date: March 2017 Contact: Name: Klaus Hasselbach Institut Néel - CNRS Phone:04 76 88 11 54 e-mail: [email protected] More information: http://neel.cnrs.fr

40 µm



28

Exploring Antiskyrmions

Introduction : An antisymmetric exchange interaction, the Dzyaloshinskii-Moriya Interaction (DMI), occurs in systems with strong spin orbit coupling and without crystallographic inversion symmetry. The DMI promotes perpendicular spin alignment and is the driving force for the stabilization of exotic spin textures like skyrmions and anti-skyrmions (Fig.1). These are quasi-particles characterized by chiral vortex-like spin configurations. Skyrmions were experimentally found in hexagonal lattices and isolated as a metastable state. Antiskyrmions, however, were up to now only investigated theoretically in dipolar magnets. We recently explored the possibility to stabilize them in magnetic ultra-thin films with DMI. Project stage in Institut Néel : We propose a fundamental pioneering work with the goal to investigate the relationship between the crystal symmetry and the DMI symmetry in ultra-thin magnetic multilayers. Optimizing the lattice symmetry at the interface between a magnetic layer and a heavy metal it should be possible to find the conditions for stabilizing antiskyrmions, requiring DMI of opposite signs along different directions. The work will be composed by different parts: - Sample growth: Epitaxial ultra-thin layers will be grown via pulsed laser deposition in an ultra high vacuum system. The crystal symmetry and properties will be investigated in-situ with RHEED (Reflection High Energy Electron Diffraction) and STM (Scanning Tunneling Microscopy) and outside the vacuum with AFM (Atomic Force Micropscopy). - Magnetic characterization: The DMI strongly influences magnetic configurations like Domain Walls (DW) and excitations like Spin Waves (SW). Magneto-optical techniques will thus be used to study the DW propagation (using Kerr microscopy) and the SW symmetry (using Brillouin Light Scattering spectroscopy) -‐ Micromagnetic simulations and analytic calculations will be performed to investigate the role of the DMI symmetry in the stabilization and in the dynamics of an isolated antiskyrmion. Collaborations : Imaging of magnetic textures at the nanoscale will be performed at the SOLEIL synchrotron and in collaboration with the LPA laboratory in Montpellier. Brillouin Light Scattering to measure the DMI anisotropy will be performed with LSPM (Villetaneuse). Micromagnetic calculations and simulations will be developed in collaboration with the Laboratoire de Physique des Solides (CNRS) in Orsay and Spintec in Grenoble. Ce stage pourra se poursuivre par une thèse : Yes Skills: This is a pioneering project, where imagination and open mind approaches are recommended. Good mathematical skills, a fundamental knowledge of quantum physics and a good basis of condensed matter physics are required. Période envisagée pour le début du stage : 01/03/2017 Contact : VOGEL Jan Institut Néel - CNRS : 0476887912 e-mail: [email protected]

Fig1: Antiskyrmion



29

Magnetic multilayers for coupled domain walls and skyrmions

General Scope:

The scope of this internship is to grow and characterize magnetic multilayers in which chiral domain walls (DW) and magnetic skyrmions may be stabilised. These multilayers, where a thin (less than 1 nm thick) Co layer is in contact with a heavy metal in a non-centrosymmetric stack, can contain chiral magnetic textures, i.e. magnetic structures where the moment rotates from one site to the next. Such chiral textures are induced by the interfacial Dzyaloshinskii-Moriya interaction (DMI), an anti-symmetric exchange interaction, favoring a perpendicular orientation between neighboring magnetic moments. It is in competition with the Heisenberg exchange interaction, that tends to align neighboring spins parallel to each other. The competition between them locally induces spiraling magnetic structures : chiral magnetic domain walls (Fig. left) and skyrmions (Fig. right). They may be moved at high velocity using magnetic fields or electric currents. In this project, we will test multilayer stacks containing two Co layers coupled by dipolar interactions, which will make the domain walls and skyrmions more stable, allowing them to move at higher maximum speeds. Research topic and facilities available:Our group has a large experience in growing and characterizing magnetic multilayer systems. We have extensively worked on Pt/Co/AlOx and Pt/Co/GdOx stacks. The goal of this internship will be to optimize the growth of stacks like Pt/Co/Ir/Co/Pt with a Co thickness of 0.6 to 1.0 nm, and an Ir thickness of about 1.0 nm. These stacks will be deposited in Institut Néel by RF sputtering. Magnetic characterization using Vibrating Sample Magnetometry and measurements of the thickness of the different layers and the interface quality will performed by X-ray reflectivity. Measurements of the domain wall velocities as a function of magnetic field will be performed using Kerr microscopy. The presence of skyrmions will also be verified. After studying the continuous layer stacks, strips some hundreds of nanometers wide and some tens of micrometers long will be nanofabricated from these stacks. They will be used to study the propagation of domain walls and skyrmions induced by short current pulses, which is very important for their potential use in high density magnetic storage. All the required techniques are available at the Institut Néel and our group Micro- and Nano-magnetism has a large experience using them. Possible collaboration and networking:Collaboration with Laboratoire de Physique des Solides (Orsay) for modelling static and dynamic properties of coupled domain walls and skyrmions Possible extension as a PhD : Yes Required skills: Good experimental skills and basic knowledge of (nano)magnetism are needed. Starting date: 01/03/2017 Contact: Name: Stefania Pizzini Institut Néel - CNRS Phone: 04 76 88 79 15 e-mail: [email protected]



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New generation of phosphors for LED lighting prepared by sol-gel method

General Scope: Lighting by "white LEDs" has become a major challenge for energy saving. However, several problems need to be overcome, the most important are: cost, quality of the white photoluminescence emission and thermal stability. Currently, all devices used, or in development, involve rare earth ions whose main drawbacks are lighting with narrow emission bands with a significant blue component and also their high cost as they are highly strategic elements due to the monopoly of their production by China. At the Institut Néel, we develop a new type of phosphors based on vitreous powders to achieve white LEDs for solid lighting. The innovative character of these aluminum borate phosphors is to produce a broadband luminescence emission throughout the visible spectrum, from color centers (structural defects) in an amorphous matrix. In addition, these phosphors are made of non-toxic and abundant, no rare earth thus making them much less expensive. The project is the pursuit of original work (thesis and patent), which has been initiated in recent years. These phosphors are synthetized by two different “chimie douce” routes: - modified pechini method (polymeric precursors) - sol-gel method (alkoxide precursors); each method leading to a master topic. Research topic and facilities available: The aim of this stage are firstly: - Understanding the origin of the emitting centers, which are related to structural defects (oxygen radicals, carbon interstitials...) in order to optimize the luminescence properties. Recent results obtained by thermal analysis (TDA-TG) coupled with mass spectrometry and 13C NMR show residual carbon groups in luminescent powders. Nevertheless, one part of the residual carbons is pyrolytic carbon (aromatic carbon), which leads to partial re-absorption of the visible emitted luminescence, and thus induces a decrease of the emission intensity. Furthermore, structural studies show that the interconnected inorganic network obtained by sol-gel route retains organic moities up to high temperatures. The optimization of the synthesis of these phosphors will be performed by sol-gel route varying chemical factors. Different metals with lower coordination number and stoichiometric ratios of molecular precursors (allowing metal complexation and polymerization of organic-inorganic network) will be tested. The change of chemical composition should enable to adjust the width of the spectral emission of luminescent for better colorimetry. A study of the different parameters of thermal treatments (heating rates, the ranges of temperature, controlled atmosphere during treatment), which are at the origin of the presence of emitting centers should be clarify. Finally, the understanding of the origin and role of emitting centers and the structural characterizations and modeling of the amorphous phase will be implemented by coupled spectroscopic studies: FTIR, UV-Vis spectroscopy, EPR, NMR, X-ray diffraction and X-ray scattering.

Possible collaboration and networking: Institut de Recherche Chimie-Paris ; INAC-CEA Grenoble Possible extension as a PhD: Yes Required skills: Chemistry in solution, knowledge on physicochemical and structural characterizations of material Contact : Pr Gautier-Luneau Isabelle Institut Néel – CNRS Phone: 04 76 88 78 04 e-mail: [email protected]/ More information: http://neel.cnrs.fr



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Fluctuations hydrodynamique en conditions extrêmes

Cadre général : De tous les fluides, l’hélium cryogénique est celui présentant la plus faible viscosité. Cette propriété est mise à profit en laboratoire pour produire des états turbulents très intenses, inaccessibles aux expériences traditionnelles. L’enjeu consiste à tester les théories de la turbulence dans des conditions optimales. Les installations cryogéniques du CERN, uniques au monde par leur puissance réfrigérante, ont permis de construire une expérience de jet d’hélium gazeux de tous les records, en particulier en terme d’intensité turbulente (nombre de Reynolds jusqu’à 107). Après une première campagne de mesure ayant permis de valider l’expérience en Juillet 2015, les prochaines campagnes sont possibles jusqu’en 2017 grâce à un financement européen. Sujet, moyens disponibles :

Nous souhaitons recruter un étudiant (stage + thèse) qui participera aux futures campagnes et conduira l’analyse physique des données turbulentes. Concrètement, une partie du travail sera consacrée à l’instrumentation et à la mise en œuvre de l’expérience. L’autre partie sera consacrée à l’analyse des données, et en particulier aux tests des lois de turbulence à très haut nombre de Reynolds (statistique des fluctuations de vitesse et de température). Des mesures complémentaires seront menées dans d’autres écoulements d’hélium, disponibles à Grenoble.

L’activité est basée à Grenoble, avec des séjours courts et réguliers au CERN. Interactions et collaborations éventuelles : L’expérience, coordonnée par notre laboratoire, est menée dans le cadre d’une collaboration inter-laboratoires et dans le prologement de la collaboration européenne EuHit (www.euhit.org). En particulier, le CERN héberge l’expérience principale mais des expériences de plus petites tailles seront mises en œuvre dans notre laboratoire.

Ce stage pourra se poursuivre par une thèse : Oui Formation / Compétences : Compétences développées: Instrumentation & Mesures bas bruit, Hydrodynamique & Turbulence, Physique des basses températures & Cryogénie, Nanotechnologie & Technique de microfabrication, Acquisition & Traitement du signal. Période envisagée pour le début du stage : indifférente Contact : Roche Philippe, Institut Néel – CNRS/UGA [email protected] (04 76 88 11 52) http://hydro.cnrs.me

T



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A single spin transistor for quantum processing

Cadre général : The realization of an operational quantum computer is one of the most ambitious technological goals of today’s scientists. In this regard, the basic building block is generally composed of a two-level quantum system (a quantum bit). It must be fully controllable and measurable, which requires a connection to the macroscopic world. In this context, solid state devices, which establish electrical connections to the qubit are of high interest. Among the different solid state concepts, spin based devices are very attractive since they already exhibit long coherence times.

Electrons possessing a spin 1/2 are conventionally thought as the natural carriers of quantum information, but alternative concepts make use of the outstanding properties of molecular magnets as building blocks for nanospintronics devices and quantum computing. Their magnetic moment, or the nuclear spin carried by a single atom, benefit from longer coherence times compared to purely electronic spins. In this context, our team combines the different disciplines of spintronics, molecular electronics, and quantum information processing. In particular, we fabricate, characterize and study molecular spin-transistor in order to manipulate[1] and read-out an individual spin[2] to perform quantum operations. [1] S. Thiele, F. Balestro, R. Ballou, S. Klyatskaya, M. Ruben, W. Wernsdorfer, Science 2014. [2] R. Vincent, S. Klyatskaya, M. Ruben, W. Wernsdorfer, F. Balestro. Nature 2012. Sujet exact, moyens disponibles : Nano-devices addressing single molecular spins will be designed and reliable methods for their realization and caracterization will be developed. Our team has a strong experience in molecular magnetism, nanofabrication, ultra-low noise transport measurements, microwave electronics and cryogenic equipment. First, the student will learn and participate to the sample fabrication using the clean room facilities of the Néel Institut. She/he will then carry out the measurements of the device at very low temperature (20mK), using one of the six fully equipped dilution refrigerators of the team, in order to create, characterize and manipulate single spin using spin based molecular quantum dot. Interactions et collaborations éventuelles : This multidisciplinary research field is based on years of collaborations with teams from different scientific and technical cultures (cleanroom, technicians, collaborations with chemists and theoreticians, ...), in the framework of European projects and different national and regional funding. Ce stage pourra se poursuivre par une thèse : Yes Formation / Compétences : M2 level We are looking for a motivated student who is interested in experiments that are challenging from the experimental point of view. Période envisagée pour le début du stage : from Feb 1st up to 5-6 months Contact : BALESTRO Franck Institut Néel - CNRS : [email protected] For more information : http://neel.cnrs.fr/spip.php?rubrique51



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Epitaxial Superconducting Quantum NanoWires

Scientific Context:

During the last decade, it has been demonstrated that superconducting Josephson quantum circuits constitute ideal blocks to build quantum bits and to realize quantum mechanical experiments. These circuits appear as artificial atoms whose properties are fixed by electronics compounds (capacitance, inductance, tunnel barrier)[1]. Up to now only aluminum polycrystalline films were used to realize the superconducting quantum circuits. These films present poor structural and electrical properties (superconducting films in the dirty limit, amorphous tunnel barrier in the Josephson junctions, amorphous native oxide…), which could limit the quantum coherence in the experiments. High quality epitaxial thin films can overcome this limitation. During the last years, through a collaboration between NEEL and SIMAP (B. Gilles team), we have successfully developed and characterized very high quality epitaxial superconducting films of rhenium. These films present very low density of defects and impurities leading, as example, to very long mean free path for the electrons and to the absence of native oxide[2]. This opens new possibilities to build superconducting quantum circuits based on nanowires. In our team we have developed original microwave quantum optics experiments coupling artificial atoms and microwave resonators[1] and we want to develop a novel generation of circuits based on such high quality material.

Figure: Epitaxial rhenium films with atomic terraces growth by MBE in SIMAP (B. Gilles).

[1] E. Dumur et al., “V-shaped superconducting artificial atom based on two inductively coupled transmons,” Phys. Rev. B, vol. 92, no. 2, Jul. 2015. [2] E. Dumur, et al, “Epitaxial rhenium microwave resonators”, IEEE on Applied Superconductivity, 26, 1501304, 2016. Description, means available: The candidate will fabricate and study novel superconducting quantum nano-circuits based on epitaxial rhenium films. In particular we plan to study ultra thin films (few nanometers thick) and superconducting nano-wires in which quantum fluctuations and nonlinearity effects could emerge. The epitaxial films will be grown in two Molecular Beam Epitaxy equipments in SIMAP and in NEEL. The nano-fabrication using lithography processes will be developed in NanoFab and PTA facilities. She/He will then carry out the dc and microwave measurements of the device at very low temperature to characterize and analyze the properties of the device. Our team has a strong experience in nanofabrication, microwave electronics and cryogenic equipment. Interactions and collaborations: Our team is part of several national networks. We are strongly collaborating with Bruno Gilles in SIMAP for the epitaxial growth of rhenium thin films. This project is financially supported by the “Agence Nationale pour la Recherche” (National French Funding Agency). This internship can be pursued toward a PhD Education / Profile: Master 2 or Engineering degree. We are seeking motivated students who want to develop novel superconducting quantum circuits based on very high quality epitaxial films. Start Period: Flexible Contact : BUISSON Olivier and NAUD Cécile Institut Néel- CNRS : phone: +33 4 56 38 71 77 email: [email protected], [email protected] Plus d'informations sur : http://neel.cnrs.fr & http://neel.cnrs.fr/spip.php?rubrique50



34

Graphene based superconducting quantum bit

Cadre général : The future of nanoelectronics will be quantum. Downscaling in electronics as now reached a point where the size of the devices (less than 10 nm) means that their quantum behavior must be taken into account. While this might be seen by some industries as a major problem this also gives a real opportunity to rethink the way electronics works and make devices with new quantum functionalities. A key building block for future quantum electronics systems is the quantum bit. Such system has two possible states (0 and 1) but they follow the law of quantum mechanics. One example is that one might build any superposition of 0 and 1. This will have implications for building future quantum computers. Sujet exact, moyens disponibles : In this work we want to build a new type of device to implement a quantum bit that we hope will have strong advantages over other competing systems. The idea is to use the know-how that has been developed in the superconducting quantum bit community over the past 20 years and integrate in the core of the system a semiconducting material coupled to superconducting contacts to bring novel electrical functionality to the device. We will use graphene, a two dimensional zero band gap semiconductor [Nov04]. The team has a strong expertise in graphene[Ren14,Han14] that will be at the core of this project. A sheet of graphene will have to be integrated into a superconducting quantum bit design [Koc07] using nanofabrication techniques as illustrated in Figure 1. Such sample will then be measured at very low temperature (20mK) in a dilution refrigerator using radiofrequency (1-10 GHz) techniques. This will allow to demonstrate that the system behaves as a two-level system and to show that its energy levels can be tuned with an electric field. After this demonstration, more involved measurements will be carried out in the following PhD project (lifetime, coherence, coherent manipulation...).

Figure 5: A Josephson Junction, i.e. a weak link between two superconducting regions, is made using graphene. Radiofrequency techniques are used to probe the system

[Han14] Z. Han et al Nature Physics 10, 380 (2014) [Koc07] J. Koch et al Phys. Rev. A 76, 042319 (2007) [Nov04] K.S. Novoselov et al Science 306, 666 (2004) [Ren14] J. Renard et al Phys. Rev. Lett. 112, 116601 (2014) Intéractions et collaborations éventuelles : The work will be carried out in the Hybrid team. The team has also several external collaborations worldwide (France, Germany, Canada). Ce stage pourra se poursuivre par une thèse (ou ce sujet est limité à un stage M2...).Yes Formation / Compétences : The internship (and the PhD thesis) will require a solid background in solid state/condensed matter physics. The work will be mainly experimental. The candidate is expected to be strongly motivated to learn the associated techniques (nanofabrication in clean room, radiofrequency electronics, cryogenics...) and engage in an hands-on experimental work. Période envisagée pour le début du stage : March 2017 Contact : Vincent Bouchiat/Julien Renard Institut Néel ; 0456387176 ; [email protected]



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Competing electronic orders in the two-dimensional limit Cadre général : Tantalum disulfide (TaS2) is a lamellar material, well-known in its bulk form to condensed matter physicists. It is prone to transformations between multiple phases, corresponding, along the z-axis, to different atomic stacking, and in the xy-plane, to charge density waves linked to various periodic lattice distortions. Accordingly a wealth of inter-dependent quantum states compete, from a Mott insulator, to a metal, and a superconductor. Recently TaS2, has been prepared in non-bulk forms, down to a single, three-atom-thick layer – becoming a true two-dimensional (2D) material. There, not only the environment of the atoms involved in phase transitions is qualitatively different from the bulk case, but also these atoms are all directly amenable to scrutiny, and TaS2's electronic doping can be extensively tuned by chemical or electrostatic gating. 2D TaS2 is thus predicted1 a unique playground to address and control a variety of quantum phases, which started to be explored with experiments two years ago.2,3 Sujet exact, moyens disponibles : The goal of the internship will be to prepare original architectures based on single- and few-layer TaS2, and to address the relationship between the structure and the vibrational properties during phase transitions, which will be induced with changing temperature. Within the usual few-month duration of the internship, the scope of the work will be on phase transitions involving the formation of charge density waves, whose signature will show up as specific phonon modes and superstructure signals in diffraction experiments. The work is meant to extend, in the framework of a PhD thesis, to the study of micrometer-scale devices with which non-conventional quantum phase transitions will be explored. A micro-transfer facility operated under an optical microscope under a clean atmosphere will be used to prepare 2D TaS2 sandwiched between two protective thin boron nitride films, following a process established at Institut Néel for other 2D materials (see Figure). The protected TaS2 will be studied with Raman spectro/microscopy down to 10 K and atomic force microscopy. Other 2D TaS2 samples, prepared under ultra-high vacuum by experts at Institut Néel, will also be studied in situ by electron diffraction down to 100 K, by Raman spectroscopy, and scanning tunneling microscopy. Références : (1) A. H. Castro Neto. Charge density waves, superconductivity, and anomalous metallic behavior in 2D transition metal

dichalcogenides. Physical Review Letters Vol. 86, p. 4382 (2001) (2) Y. Yu et al. Gate-tunable phase transitions in thin flakes of 1T-TaS2. Nature Nanotechnologies Vol. 10, p. 270 (2014) (3) E. Navarro-Moratalla et al. Enhanced superconductivity in atomically thin TaS2. Nature Communications Vol. 7, p. 11043 (2016) Interactions et collaborations éventuelles : The student will join a team gathering experts in materials science, optical spectroscopy, condensed matter physics, surface science, and first principles calculations. The proposed work is linked with several national-scale programs, and will involve collaborations inside and outside the lab with experts in high resolution microscopy and photoelectron spectroscopy (including at synchrotron sources). Ce stage pourra se poursuivre par une thèse. Formation / Compétences : Strong background in condensed matter physics and strong motivation for experimental work are required. Période envisagée pour le début du stage : March 2017 Contact : Johann Coraux/ Nedjma Bendiab Institut Néel - CNRS : [email protected]/ [email protected] d'informations sur : http://neel.cnrs.fr

Figure 6: Optical image of graphene sandwiched between two hBN layers.

30 µm



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Large scale spin-based quantum information processing in Si28 based semiconductors

Context : In quantum nanoelectronics, a major goal is to use quantum mechanics in order to build efficient nanoprocessors. This requires the ability to control electronic phenomena in a nanostructure at the single electron level. In this context, the electron's spin has been identified as an appropriate degree of freedom for efficient storage and manipulation of quantum information. The defined building block of this quantum computer strategy is the spin of a single electron trapped in a quantum dot. The implementation of the system as a quantum nanoprocessor resembles the classical circuit boards contained in a classical computer. In dot systems, all the basic operations of a quantum nanoprocessor have been demonstrated for GaAs spin qubits. Intense experimental effort is

Figure: Artistic view of the sample envisioned to realize a multi-dot structure to perform operations and algorithms with a few electron spin qubits.

nowadays invested in Si28 semiconductor where coherence properties are the best observed for electron spin qubits and which offers compatibility with CMOS technology used in microelectronics. Objectives and means available : The goal of the project is to design and to measure a network of coupled quantum dots where single spin manipulation and coherent interaction between adjacent electron spin qubits can be implemented. The ultimate goal will be to perform small quantum information protocols or algorithms with few spin qubits such as quantum error correction or to displace the electron within the network. All the samples will be fabricated in CEA-LETI with a state of the art Si facility to enable maximum output and reproductibility. To control and manipulate the electron spin coherently, the applicant will benefit from the long-standing expertise of the Neel-group in AlGaAs based electron spin qubits (computer control, low temperature cryogenics, low-noise electronics, Radiofrequency electronics). Interactions and collaborations: This work is part of a large collaborative effort between the CEA-INAC, CEA-LETI and CNRS-Institut Néel to develop and push the technology of spin qubit in Si28 and investigate its potential scalability. Skills and training : The experimental project relies on the knowledge accumulated in the field of few-electron quantum dots and its new implementation in Si devices. All along this project, the candidate will acquire important skills in the field of condensed matter physics: nanofabrication, cryogenics at mK, low-noise electronics, computer control… Foreseen start for the beginning of the internship: From January to April 2016 Possibility of continuation as a PhD on the same subject with funding already secure. Contact : Tristan Meunier Institut Néel/ CNRS- Université Joseph Fourier [email protected] plus d'information sur : http://neel.cnrs.fr



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Suspended graphene and nanotubes for low temperature opto-electronics.

Cadre général : Molecular electronics provides new concepts for devices with unprecedented functionalities. Due to their low dimension, carbon nanotubes (CNTs) and graphene exhibit remarkable electronic, and optical properties allowing the transduction of optical information into an electrical one. However, their conductance is highly sensitive to their environment. For example grafting optically active molecules on nanotubes realizes an optically activated transistor (1). In particular, coupling with a substrate leads to strong modification of heat transfer, phonon lifetime, doping. We therefore suspend graphene and nanotubes to reach a regime of low coupling with substrate phonons and charges. This is expected to provide an optimized situation to detect small signals from molecules grafted on the nanotube for optoelectronics at low temperature. Moreover it enables to observe out of equilibrium regime visible both by transport and Raman spectroscopy. Such regime leads to different temperatures of phonons and electron baths. The electron-phonon coupling plays a major role in this regime but is not yet fully understood. It is crucial for applications to understand which coupling is involved and whether it is dependent on the transport regime (low bias vs saturation regime). Sujet exact, moyens disponibles:

The internship aims at investigating the out-of-equilibrium regime in suspended nanotubes and graphene (2). To fit the timescale of the internship, the simplest geometry will be used at room temperature: a two laser setup will be used to heat the system while doing Raman spectroscopy at the same point (see figure). Raman imaging will provide information about spatial distribution of hot phonons and will allow inferring issues on electron-phonon coupling, strain and heating in the system (3,4). The student will be in charge of the full spectroscopic characterization of the devices. She/He will participate to the fabrication of the substrates and the development of the next substrates with electrical wiring. The simultaneous use of Raman spectroscopy and electron transport at this single nano-object level is almost unique and promising compared to conventional methods used separately until now. The setup in ambient conditions is fully operational. The student will participate to

the development of the 10K setup.

Références : (1) Chen et al., Biologically Inspired Graphene-Chlorophyll Phototransistors with High Gain. Carbon N. Y. 63, 23 (2013). (2) Lazzeri et al., Electron Transport and Hot Phonons in Carbon Nanotubes, Phys. Rev. Lett. 95, 236802 (2005). (3) Cepellotti et al., Phonon hydrodynamics in two-dimensional materials. Nature Comm., 6. (2015). (4) Balandin et al., Thermal properties of graphene and nanostructured carbon materials, Nat. Mater. 10, 569 (2011). Interactions et collaborations éventuelles : The student will join the Hybrid team gathering experts in materials science, optical spectroscopy, condensed matter physics, mesoscopic transport. Close collaborations outside the lab involve material synthesis at CIRIMAT, Toulouse, molecular synthesis at DCM, St Martin d’Hères, photoluminescence spectroscopy at Laboratoire Pierre Aigrain, Paris. This internship can be pursued as a PhD. Formation / Compétences : A master 2 level in Condensed Matter Physics or Nanosciences is required along with motivation for experimental work and cryogenic setup development. Période envisagée pour le début du stage : February/March, 2017 Contact : Nedjma Bendiab, Laëtitia Marty Institut Néel - CNRS : [email protected] / [email protected] More information on : http://neel.cnrs.fr/spip.php?rubrique621

Figure 7: Schematic of a two lasers experiment.



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Three-dimensional experimental study of a quantum fluid:

What is the dynamic of the quantum vortex? Cadre général : While liquefying the most common helium isotope at a temperature below 2.17K, a very uncommon liquid phase called HeII appears. This phase is made of the superposition of a normal and a superfluid that interact through mutual friction between the normal fluid and the quantum vortices that are “carrying” the vorticity of the superfluid. In 2006, a team of American researchers has discovered how to trap micron-size particles on the core of these vortices. Therefore, we can now study their dynamics using imagery based measurement techniques. The research project is to adapt the three-dimensional Lagrangian Particle Tracking (3D-LPT), cutting edge technology developed in standard fluid mechanic, to the experimental study of these quantum vortices. I propose a series of experimental setups that will allow us to probe the properties of quantum vortex tangles of different number density. These experiments will help us understand the dynamic of this peculiar object together with the interactions vortex/vortex, vortex/particle, while varying the proportion fluid/superfluid. Sujet exact, moyens disponibles : We want to recruit a student (first as an intern, then as a PhD) that will acquire and analyze the optical data mentioned above. The internship and the first half of the PhD will be focused on the instrumentation (temperature measurements, optical setup…) and the global setup of the experiment (acquisition system, particle generation…). A postdoctoral research associate will help concerning the 3D optical measurements. The second half of the PhD will be used to refine the data analysis and the experimental protocols. In particular, the dedicated optical cryostat will be setup on a spinning table to allow us to generate polarized quantum vortex tangles (oriented preferentially along the axis of rotation of the system). This project is financially supported by the ANR (“Agence Nationale de la Recherche”) Interactions et collaborations éventuelles : The entire work is located in Grenoble in the Institut Néel (CNRS), but collaborations with ENS-Lyon, LEGI (Grenoble) and the Max Planck Institute for Dynamics and Self-organization (Göttingen - Germany) are planned in the context of 3D measurement techniques and normal fluid comparison. Additionally, we expect a strong interaction with our neighboring institute CEA/SBT. Ce stage pourra se poursuivre par une thèse. Formation / Compétences : Physics and/or Engineering (hydro, instrumentation, programing) Période envisagée pour le début du stage : Indifferent Contact : Gibert Mathieu Institut Néel - CNRS : +33 (0)476-88-10-13 [email protected] Plus d'informations sur : http://neel.cnrs.fr & http://www.gibert.biz

3D Lagrangian trajectories obtained by LPT in a turbulent flow



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Recherche de nouveaux supraconducteurs à haute température critique Cadre général : La supraconductivité non-conventionnelle à haute température critique apparait lorsqu’un composé bidimensionnel ayant un ordre antiferromagnétique avec une température de Néel (TN) élevé et un faible moment magnétique est dopé. Ceci est le lié à la forte interaction d'échange, responsable de l'antiferromagnétisme mais aussi de la supraconductivité. En particulier c'est le cas des cuprates et des chalocgénures et arséniures de fer. Donc une stratégie raisonnable pour chercher des nouveaux supraconducteurs non-conventionnels à haute température critique est de sélectionner des matériaux présentant ces propriétés, les synthétiser et les doper. En particulier les composés au chrome sont connus pour avoir un antiferromagnétisme fort. Ceux ayant en plus une basse dimensionnalité sont difficiles à synthétiser, ce qui est un obstacle important, mais qui nous permet aussi d'être les parmi les premiers à les étudier pour comprendre leur physique. Celle-ci peut être très riche, indépendamment du fait de l’obtention de la supraconductivité ou non (effet Kondo Orbital dans CrSe2 [1]; Fluctuations quantiques à 600 K dans CrRe [2].) Même s’il y a quelques années, songer à trouver de la supraconductivité dans des composés au chrome rendait les experts sceptiques, sa découverte dans CrAs sous pression [3], permet maintenant d’élargir ce type d'étude. Sujet exact, moyens disponibles : Nous proposons en premier lieu d'essayer le dopage de composés type Ruddelsden-Popper Æn+1CrnO3n+1 (où Æ est un alcalino-terreux; voir figure). Nous avons déjà synthétisé les phases mères n=1, 2 et 3, et nous avons compris, grâce à des interactions entre expérimentateurs et théoriciens, leur physique. La synthèse de ces oxydes se fait à haute pression et haute température, en profitant de l’infrastructure très performante du laboratoire. Les propriétés cristallographique, électrique, magnétique, ainsi que la chaleur spécifique et l'expansion thermique seront sondés grâces aux différents appareils de caractérisation dont dispose l’Institut Néel. Des mesures sous très haute pression complèteront l’étude. Interactions et collaborations éventuelles : Des mesures utilisant la diffusion des neutrons (ILL) et ou des rayons X sur synchrotron (ESRF) seront aussi nécessaires à moyen terme pour comprendre l’ensemble des propriétés. D'autre part, ce sujet bénéficiera des interactions avec les théoriciens de l'Institut Néel ou de l'étranger. [1] M. Núñez et al. Phys. Rev. B. 88 [2013] 245129. [2] D. Freitas et al. Phys. Rev. B. 92 [2015] 205123. [3] Wu Wei et al. Nature Comm.5 [2014] 5508. Ce stage pourra se poursuivre par une thèse (ou ce sujet est limité à un stage M2...): Oui. Formation / Compétences : Une bonne connaissance de la physique de la matière condensée est souhaitée. Période envisagée pour le début du stage : mars-avril 2017 Contact : Núñez-Regueiro, Manuel MCBT/Institut Néel - CNRS : tél : 04 76 88 78 38 mel [email protected] Toulemonde, Pierre PLUM/Institut Néel - CNRS : tél : 04 76 88 74 21 mel [email protected] Plus d'informations sur : http://neel.cnrs.fr



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Study of the physical properties of new unconventional superconductors under extreme conditions of pressure

Cadre général : The mechanism of high Tc superconductivity remains an open question in condensed matter physics. Such superconductors show record Tc values of 135K for Cu based families and 55K for iron based arsenides and chalcogenides at ambient pressure. The electron-phonon coupling is too weak in these layered materials to explain their high Tc, other mechanism such as spins fluctuations has to be involved. The comparison of the physical properties of the different families helps to find the relevant parameters to reach high Tc superconductivity. In that sense, the use of high pressure (HP) to explore their phase diagram is a good way to probe the physics of the parent and superconducting phases. We actually use this approach in our laboratory to study FeSe (see fig. 1a).

Sujet exact, moyens disponibles : More recently, we were interested in systems were Fe2Se2 unit blocks are separated by A2MO2 (Ae=Ba,Sr,Ca or K and M=Co or Cu) (see fig. 1b) because increasing distance between Fe planes favors higher Tc. By extension we try currently to synthesize pure Fe- or pure Cu-based layered systems with A2CuO2Cu2As2 and A2FeO2Fe2As2 compositions. An intermediate system, Ba2Ti2Fe2As4O, where Fe2As2 layers are separated by Ti2O sheets, is also interesting because it shows two coexisting states: superconductivity in Fe planes and a charge or spin-density wave in Ti based sheets. During the internship, we will focus on one of these systems to characterize its physical properties at ambient pressure and study how they change under extreme condition of pressure. In particular we will combine structural (by x-ray diffraction in a diamond anvil cell), phonons (by Raman spectroscopy) and transport measurements (in a diamond Bridgman anvil apparatus) under HP.

(a) (b) (c) Fig.1 : (a) Pressure temperature phase diagram of FeSe (Sun et al. Nat.Comm. 7, 12146 (2016)); (b) and (c): Crystallographic structures of (Ba,K)2CuO2Fe2As2 (Dai et al. Chin. Phys. B 25, 077402 (2016)) and Ba2Ti2Fe2As4O (Wu et al. Phys.RB 89, 134522 (2014)).

Interactions et collaborations éventuelles : Since the discovery of superconductivity in iron-based compounds, an important knowledge of this family has been developed in our laboratory. The candidate will benefit of it and will have the opportunity to interact with several collaborators at NEEL Institute but also outside from Grenoble.

Ce stage pourra se poursuivre par une thèse (ou ce sujet est limité à un stage M2...) : Yes. Formation / Compétences : The candidate must have a good background in solid state physics, crystallography and material science. In addition he has to be motivated by working with high pressure experimental setups requiring precision and skill. Période envisagée pour le début du stage : April 2017. Contact : TOULEMONDE Pierre and NUNEZ-REGUEIRO Manuel Institut Néel - CNRS : 04 76 88 74 21, [email protected]; 04 76 88 78 38, [email protected] Plus d'informations sur : http://neel.cnrs.fr



41

Glass Nanomechanical Resonators in the Quantum Ground State

Context: Keywords: Quantum engineering, quantum ground state, superconducting qubits, two-level systems, glass

Highly motivated students are sought for an ERC-funded project devoted to identifying the universal low energy excitations of glass. These excitations, thought to be two level systems (TLSs) formed by atoms or groups of atoms tunneling between nearly equivalent states, will be probed on the individual level for the first time. This will allow us to make a microscopic test of the controversial “tunneling model” of glass. Objectives and means available:

In order to access individual TLSs, a glass nanomechanical resonator will be cooled to its quantum ground state around 1 mK. This will be achieved using a new state-of-the-art cryostat. Only a few research groups worldwide have succeeded in cooling a mechanical resonator to the ground state, and most of them use active cooling schemes in which only the mechanical mode of interest is cold. In contrast, we will draw on our expertise in ultra-low temperature measurements to cool the entire mechanical resonator to 1 mK.

Ultimately, we are interested in properties of quantum matter. In particular, the identity of the TLSs will be investigated by making the first measurements of individual TLSs inside a mechanical resonator. The quantum state of the resonator will be controlled using a qubit to enable these measurements. First we will look for a signature of an individual TLS in spectroscopic measurements of the ground-state glass resonator. Then we will use quantum control of the mechanical resonator to in turn control and measure the quantum state of the TLS. This will yield information about the TLS and a test of the “tunneling model” mentioned above.

Figure: Intrinsic tunneling two level systems (TLSs) inside a glass nanomechanical resonator. The mechanical resonator will be cooled to the quantum ground state to enable measurements of the individual TLSs.

Possible collaborations and networking: This work will involve collaboration and interactions with high profile researchers at the

Institut Néel, elsewhere in Europe and in the United States. Required profile: The student should have a strong interest in fundamental research and making challenging measurements at very low temperatures, as well as a thorough understanding of quantum theory at the Master’s Degree level. Ce stage pourra se poursuivre par une thèse financée. Période envisagée pour le début du stage : Flexible Contact : Andrew Fefferman Institut Néel - CNRS : 04.76.88.90.92 [email protected] Plus d'informations sur : http://neel.cnrs.fr/spip.php?rubrique69&lang=fr



42

Fibered Nano-Optics Tweezers for Biological Applications

Since their introduction in 1986, optical tweezers become a standard tool for non-invasive manipulation in biology, chemistry, and soft-mater physics. In this context we have developed an original approach based on the use of optical fiber nano-tips, including the experimental and numerical tools for quantifying the optical forces acting on trapped particles. Recently we have demonstrated stable and reversible trapping of dielectric micro- and nano-particles. A further challenge is the application of our device to biological applications. Fiber-based tweezers have some specific advantages with respect to beam-focusing tweezers, more widely applied in bio-physics: the optical fiber tips can penetrate the biological cells, the illuminated region can be limited and more sophisticated laser beams can be used. The aim of this project are to realize force and spectroscopic (fluorescent) measurements inside living cells and in particular for neuronal cells (mainly neurone and astrocytes). We will investigate the mechanical and electrical signalization pathways during cells differentiation and the feedback (impact) of the micro- environment on the cultured cells. The aim of the internship is to adapt and use the existing optical fiber nano-tweezers for force measurements inside neurons. Electrical signals will also be followed by the synchronous detection and manipulation of fluorescent voltage sensitive nano-objects along the cell membrane. The internship is mostly experimental, but straightforward theoretical considerations will be required for the understanding and analysis of experimental results. The student will get deeper insight into the fields of photonics, optical forces, and biophysics. The internship is part of a recent collaboration of two scientists both from Institut Néel but with complementary backgrounds. Thus it will be co-supervised by Jochen Fick, specialist in photonics at opticial trapping, and Cécile Delacour , specialist in bio-physics. The training will take place in Institut Néels new Nano-physics-building with access to BioFap facilities including the cell culture platform. Possible extension as a PhD: Yes Required skills: The student must be highly motivated by experimental work, and should have basic skills in optics and biophysiscs. Starting date: as soon as possible Contact: Jochen Fick and Cécile Delacour Institut Néel - CNRS e-mail: [email protected] / [email protected] More information: http://neel.cnrs.fr



43

Optical trapping for biological applications

General Scope: Since their introduction in 1986, optical tweezers become a standard tool for non-invasive manipulation in biology, chemistry, and soft-mater physics. In this context we are developing an optical tweezers based on strong laser beam focusing. This device will be complementary to the optical fiber-based tweezers which was recently developed at Institut Néel. The system to develop will allow performing fluorescence microscopy or FRET imaging in parallel to optical trapping. We aim to develop optical tweezers, i.e. with force measurement and feedback, so as to perform force spectroscopy on single molecules as pictured in Illustration 1. Our research in that field targets the development of synthetic molecular machines. We focus at deciphering the folding pathway of DNA-nanostructures called DNA origami that can be algorithmically programmed to form complex shapes. This step is crucial of ones want to self-assemble nano-objects able to change shapes in a controlled fashion. Research topic and facilities available: The basic part of the optical tweezers is set-up. The aim of the internship is to implement complementary modules (e.g. for force measurements) and to optimize its operation. The work includes optical trapping experiment of micro- and nano-particles and force measurements on trapped particles. The internship is mostly experimental, but straightforward theoretical considerations will also be required for the understanding and analysis of experimental results. The student will get deeper insight into the fields of photonics, optical forces, and spectroscopy. The internship will be co-supervised by Jochen Fick, specialist in photonics and optical trapping, and Herve Guillou , specialist in bio-physics. The training will take place in the new Institut Néel's BioFab facilities, with access the cell culture platform. Possible collaboration and networking: Ongoing collaborations include groups in Bordeaux, Paris, Oxford, and Dijon Possible extension as a PhD: For excellent students an extension as a PhD is possible. Required skills: The student must be highly motivated by experimental work and have good programming skills. Knowledges in optics and biophysics are a plus but are not required. Contact: Name: GUILLOU Hervé and FICK Jochen Institut Néel - CNRS e-mail: [email protected] / [email protected] More information: http://neel.cnrs.fr

Illustration 1: Representation of a single molecule experiment using optical tweezers to understand the functionning of the DNAP

enzyme (from Bustamante Nat. Rev 2000)



44

Evaporation in a nanoporous material: from local to collective

General Scope: How confinement at a nanometer scale affects condensation and evaporation of fluids in porous materials is an active field of research. The challenge is to understand the different microscopic processes at stake depending on connectivity and disorder of the host material, nature of the fluid, temperature,… In this context, we use helium at cryogenic temperatures as a model fluid, exploiting its specific properties to obtain far-reaching results. Indeed, helium offers a nearly unique opportunity to couple high resolution thermodynamic measurements with optical observations over a broad temperature range. The power of our approach is evidenced by results obtained in Vycor, a disordered porous glass with a sponge topology [Europhys. Lett. 101, 16010 (2013)]. A strong light scattering signal on evaporation is observed at low temperatures, but disappears as the temperature is increased, suggesting an evolution from a collective to local evaporation mechanism, consistent with a crossover from collective percolation to thermally activated cavitation. Confirming this interpretation and understanding the conditions for this crossover is an important challenge, in particular related to the characterization of porous materials using so-called condensation isotherms. This led us to develop numerical simulations to analyze the optical signature of a percolation process. We predict that the scattering signal sensitively depends on the location and density of germs. Coupling these predictions to a phenomenological model of evaporation in a random network of pores qualitatively accounts for our previous observations.

A disk of nanoporous Vycor in its experimental cell, detection of

heterogeneous evaporation within the sample, simulated microscopic distribution

of vapor for a mixed scenario cavitation/percolation

Research topic and facilities available: The goal of this internship is to go beyond this qualitative agreement by performing and analyzing new, dedicated, experiments in Vycor, using either cryogenic helium or hexane or carbon dioxide at room temperature as a fluid. In both cases, the existence and range of spatial correlations will be systematically studied by using small angle light scattering. The intern will adapt and/or improve existing set-ups to perform small angle light scattering measurements. He will also design and develop an automatized fluid control system. He/she will work on the optical detection schemes, perform the experiments, and compare his/her results to our theoretical model. Possible extension as a PhD: yes Required skills: the candidate should have a background in condensed matter physics, with knowledge of classical optics, and be interested by both experimental aspects and fundamental questions. Beyond this project, the student will have opportunities to participate to our on-going research on condensation in ordered porous materials at low temperatures. Starting date: from January to March 2016 Contact: Name: Panayotis Spathis / Pierre-Etienne Wolf (Institut Néel – CNRS) E-mail: [email protected] / [email protected] For more information: http://neel.cnrs.fr/spip.php?rubrique162 or better: drop by the lab!



45

Novel magnetic phases in frustrated fluoride compounds

Cadre général : Geometric frustration has become a central challenge in contemporary condensed matter physics. It arises in magnetic systems from the impossibility to minimize simultaneously all the pair-wise exchange interactions because of constraints imposed by the topology of the lattice (see for example Fig. 1). Some highlighted results are the discovery of exotic magnetic phases, characterized by the existence of highly degenerate ground states and the absence of conventional long range order, such as spin-liquid phases. The spin-ice phase has especially retained attention: it is observed in rare earth oxides like Ho2Ti2O7 or Dy2Ti2O7, where the spins occupy the sites of a pyrochlore network (a lattice of corner-sharing tetrahedra, see Fig. 2). In the spin-ice ground state, two spins point inside a tetrahedron and two spins point outside, a feature known as the “ice-rule”, in close analogy with the proton position in water-ice. Magnetic excitations above the ground state could be identified as magnetic monopoles [1]. Based on the extensive knowledge of these compounds, we are interested in new systems, fluorides, with the modified pyrochlore structure AM2+M′3+F6 (where A is typically an alkali-metal ion, and M2+

and M′3+ are usually transition-metal ions, e.g., Ni2+, Cr3+). In this new family the M2+ and M′3+ ions occupy the sites of a pyrochlore lattice but are randomly distributed. Anderson [2] showed that minimization of the Coulomb interaction in such a system creates a distribution of ions that obeys the “ice rules” : each tetrahedron consists of two ions M2+ and two ions M′3+ in arbitrary positions, thus being the realization of a “charge ice” expected to exhibit a new type of magnetic behavior.

[1] see for example Castelnovo et al. Nature 451, 42 (2008)

[2] Anderson, Phys. Rev. 102, 1008 (1956) Sujet exact, moyens disponibles : Preliminary measurements on three fluoride compounds (KNaCrF6, CsCoCrF6, CsMgCrF6), synthesized at Oxford University, show the absence of long-range magnetic order down to 1.8 K, confirming the presence of frustration and the possible existence of unconventional magnetic states. During the internship, the magnetic properties will be measured down to very low temperature (70 mK), using SQUID magnetometers equipped with dilution refrigerators developed at the Institut Néel. The objective will be to determine the magnetic ground state stabilized at very low temperature in these systems. The student will gain knowkledge of all the aspects of the experimental set-up, including cryogenic techniques and electronics. Further measurements such as heat capacity measurements, as well as neutron scattering and high frequency ac susceptibility with our collaborators are also planned to get a deeper insight into the magnetism of these compounds. Interactions et collaborations éventuelles : Collaboration with Sylvain Petit (LLB Saclay – neutron scattering measurements) and Sean Giblin (Cardiff University, UK - high frequency susceptibility). Ce stage pourra se poursuivre par une thèse. Formation / Compétences : Master 2 Physique Période envisagée pour le début du stage : à partir de Janvier 2017 Contact : Lhotel Elsa Institut Néel - CNRS : 04.75.88.12.63. , [email protected] Plus d'informations sur : http://neel.cnrs.fr/spip.php?rubrique1196

Fig. 2: Pyrochlore lattice

AF AF

AF

Fig. 1: Ising spins in antiferromagnetic interactions in a triangle



46

Coherent quantum phase-slips in Josephson junction chains measured in a quantum bit

General Scope: The Josephson effect in large Josephson junctions has given rise to celebrated applications such as the DC and RF SQUIDs which operate as supersensitive magnetometers, single flux quantum logic circuits and high precision Josephson voltage standards. By decreasing the junction size of the Josephson junction, the superconducting phase undergoes quantum fluctuations that manifest themselves in form of windings by 2π, so called quantum phase-slips. The realization of a large coherent quantum phase-slip amplitude might have possible applications in quantum metrology.

Ebeam image of a Fluxonium qubit.

Research topic and facilities available: By microwave measurement techniques we would like to study the coherence of quantum phase-slips in a circuit realizing a quantum bit configuration. We have a new dilution refrigerator equipped with a working microwave measurement set-up enabling to do time-dependent measurements of the qubit state. Further on we fabricate our samples at the nanofabrication facility of the Néel Institute. During this internship the Master student will learn about the theory of quantum circuits, the fabrication process and also the measurement of a qubit. Interactions and collaborations: We work in close collaboration with the theoretical group of Frank Hekking and Denis Basko from LPMMC in Grenoble. This project is funded by a grant of the European Research Council. Possible extension as a PhD : yes Required skills: Master 2 or Engineering degree. We are seeking motivated students who want to take part to a state of the art experiment and put some efforts in the theoretical understanding of quantum effects in superconducting circuits Starting date: 01/03/2017 Contact: Wiebke Guichard Institut Néel - CNRS Phone : 04 56 38 70 17 e-mail: [email protected]



47

Charge detection by electrostatic force microscopy in quantum devices

Cadre général : Quantum point contacts (QPC) are quasi-one-dimensional channels defined by metallic gates in high-mobility semiconductor heterostructures. In addition to quantized conductance plateaus, Coulomb interactions in the channel lead to an anomalous feature below the first plateau called the “0.7 anomaly”. Despite intensive theoretical and experimental efforts during the last fifteen years, this feature still remains unexplained. To elucidate the complex interacting electron state responsible for this phenomenon, original experiments are necessary to provide new kind of information. We propose to use electrostatic force microscopy (EFM) to probe the most probable but still debated scenario of a spontaneous electron localization due the strong Coulomb interactions at low density. Combined with another technique called scanning gate microscope (SGM), we will unambiguously verify the presence of localized charges and answer this long-standing question on the most important quantum device.

Our scanning probe microscope uses a quartz tuning fork (TF) as force sensor and the sharp metallic tip from a commercial EFM cantilever. The force detection limit is in principle well below a single electron charge when the TF is at liquid helium temperature and if a cryogenic current amplifier is integrated in-situ with the TF. We will first start these EFM experiments with quantum dots (QD) where the Coulomb blockade phenomenon is well known, and then move to the puzzling case of QPC. The objective of the internship will be to optimize the force sensitivity of the EFM microscope down to a single electron charge using QD as test samples. The perspectives for a PhD thesis will be to carry out combined EFM and SGM experiments on QPC and to develop new experiments under large parallel magnetic field to probe the spin properties of the complex electron state in the QPC. Sujet exact : The master student will develop and operate the EFM and SGM experiments, combining cryogenics, electronics, and scanning probe microscopy. These complex experiments require good experimental skills and a high motivation. The devices are prepared by collaborators in Paris from high mobility GaAs/AlGaAs heterostructures. Interactions et collaborations éventuelles : Marc Sanquer (CEA, Grenoble) and Benoit Hackens (UCL, Belgium). Ce stage pourra se poursuivre par une thèse : A PhD thesis is possible if a funding is obtained. Formation / Compétences : Master in condensed matter physics and/or nanosciences. (Matière quantique, Nanophysique, etc...) Période envisagée pour le début du stage : February 2017 Contact : Hermann Sellier Institut Néel CNRS-UGA, office: D418, tel: 04 76 88 10 86 [email protected] http://www.neel.cnrs.fr/spip.php?article3282



48

Scanning gate microscopy on graphene quantum point contacts

Cadre général : Graphene is a monolayer of carbon where unique electronic properties of massless Dirac fermions result from a linear dispersion relation around the so-called Dirac points. At zero magnetic field, the absence of energy gap makes the fabrication of nanostructures difficult using traditional metal gates. In large magnetic fields however, the formation of Landau levels creates gaps in the spectrum, such that the conducting edge channels follow the electrostatic potential of the gates. Recently, we demonstrated the operation of quantum point contacts (QPC) in the integer and fractional quantum Hall regime using a high mobility graphene encapsulated between boron-nitride flakes. These samples are fabricated in the laboratory with a dedicated transfer setup allowing us to pick-up and release the graphene and boron-nitride flakes one after each other to build a vertical stack. Two lithography steps in clean room are then necessary to pattern the stack by etching and to deposit the electrodes. During the internship, the student will learn this sample fabrication and then use a scanning probe microscope at low temperature and under high magnetic field to investigate the physics of graphene quantum point contacts in the quantum Hall regime. In particular, anomalous quantum Hall plateaus have been observed that may originate from equilibration of the chemical potential between edge states in the bulk and below the gates, an hypothesis that we would like to investigate further by imaging the current paths by scanning gate microscope (SGM). This technique consists in tuning locally the electrostatic potential inside the graphene with an AFM tip and by recording simultaneously the effect on the device conductance, such as to build a map of the transmitted current through the device. Perspectives for a PhD thesis could be an SGM study of quantum Hall interferometers induced by the SGM tip itself close to a QPC. Sujet exact : The master student will fabricate his/her own devices by exfoliation of graphite and boron-nitride crystals, transfer of flakes to fabricate heterostructures, and clean-room nanofabrication. The student will also use our cryogenic AFM microscope to carry out SGM experiments, first, on existing QPC devices made out of GaAs/AlGaAs heterostructures, and then, on his/her own graphene devices. The student should be interested both by sample fabrication and by complex experiments. Interactions et collaborations éventuelles : This work will be supervised jointly by Hermann Sellier and Benjamin Sacépé (QNES team). Ce stage pourra se poursuivre par une thèse : A PhD thesis is possible if a funding is obtained. Formation / Compétences : Master in condensed matter physics and/or nanosciences. (Matière quantique, Nanophysique, etc...) Période envisagée pour le début du stage : February 2017 Contact : Hermann Sellier Institut Néel CNRS-UGA, office: D418, tel: 04 76 88 10 86 [email protected] http://www.neel.cnrs.fr/spip.php?article4205



49

Résolution de nouvelles structures cristallines par Movie-Tomography en

Diffraction Electronique

Cadre général : En science des matériaux, il est primordial de bien connaître la structure cristalline d’un matériau pour pouvoir comprendre ses propriétés physiques, et la diffraction électronique est un outil idéal pour caractériser la structure de la matière. Cependant, certains matériaux s’amorphisent au bout d’une quelques minutes sous faisceau électronique, ce qui requiert des techniques de caractérisation structurales à la fois efficaces et rapides. Une technique adaptée en voie de développement est la tomographie dans l’espace réciproque par enregistrement d’un film, ou « Movie-Tomography ». Sujet exact, moyens disponibles : En microscopie électronique en transmission, la diffraction électronique est l’un des nombreux modes de travail pour étudier localement la matière, et les derniers développements autour de la cristallographie aux électrons permettent de résoudre tout type de structure cristalline. Cependant, l’enregistrement des données est relativement long (de l’ordre de l’heure et demi), et lorsque l’on a affaire à des matériaux susceptibles de s’amorphiser sous le faisceau, il faut travailler avec des techniques alternatives permettant l’enregistrement d’un jeu de données complet en un temps très restreint. Pour cela, nous proposons la mise en œuvre d’une méthode appelée « Movie-Tomography », qui consiste à se positionner sur une zone du matériau à étudier, puis tilter en continu le porte-échantillon sur toute sa gamme de tilt, tout en enregistrant un film dans l’espace réciproque. Ensuite les différents clichés de diffraction électronique constituant le film sont extraits, puis exploités par les différents logiciels de cristallographie permettant l’extraction des intensités des réflexions de Bragg et ainsi la résolution de la structure. Le stage consiste donc à résoudre les structures de nouveaux matériaux pour l’énergie par Movie-Tomography. Nous étudierons l’influence des différents paramètres d’acquisition sur la précision des données. En guise d’exemple, la figure ci-dessus présente les premiers résultats de cette technique appliquée sur le composé Na2VO(PO4)2 : A gauche : 2 coupes du réseau réciproque avec les réflexions de Bragg indexées, conduisant à la détermination de la maille et du groupe d’espace. A droite : premier résultat de modèle structural obtenu sur le composé Na2VO(PO4)2 par movie-tomography. Interactions et collaborations éventuelles : Avec la chimiste qui synthétise les matériaux et les microscopistes de l’Institut Néel. Ce stage pourra se poursuivre par une thèse (ou ce sujet est limité à un stage M2...) : Oui, par une demande de financement auprès d’une école doctorale. Formation / Compétences : Il faut un bon niveau en cristallographie et en chimie du solide. Période envisagée pour le début du stage : Janvier à juin 2017 Contact : Lepoittevin Christophe Institut Néel - CNRS : tél : 04 76 88 71 92. mail : [email protected] Plus d'informations sur : http://neel.cnrs.fr



50

Quantum Hall interferometry in high mobility Graphene

Graphene is a 2D material that has attracted a huge interest since its discovery in 2005. Its gapless linear band structure that mimics massless Dirac fermions has led to the discovery of a wealth of new exciting transport properties. Moreover, the possibility to engineer very high mobility graphene devices in which electrons can travel in a ballistic fashion makes graphene the perfect playground to investigate new quantum coherent phenomena and interaction effects in the integer and fractional quantum Hall regimes.

The goal of the internship is to study an electronic analogue of the optical Fabry-‐Pérot interferometer in the quantum Hall regime of graphene. In the quantum Hall effect, electron transport is confined in one-‐dimensional channels that propagate along the edges of the sample. The use of electrostatic gate electrodes enables the control of their path to modify the interference pattern, and also the realization of constrictions (quantum point contacts [1]) that act as semi-‐reflecting mirrors for electron wave packets. These two basics elements are the keys to engineer quantum Hall interferometers (see figures). During the internship, the student will learn the van-‐der Waals pick-‐up technique used to make high mobility graphene devices and carry out measurements on state-‐of-‐the-‐art devices to unveil quantum interferences. To enter the quantum Hall regime and study the physics of quantum Hall interferometers, low-‐noise quantum transport measurements will be performed at very low temperature (~10mK, dilution fridge) and high magnetic field (18T). The student will be involved at all levels, from the device fabrication process, to the transport measurements at very low temperature and high magnetic field, to the data analysis and interpretation. For the PhD perspective, efforts will be focused on two important objectives, namely investigating the nature of the fractional quantum Hall effect with interferometers, and the interplay between the quantum Hall effect and superconductivity. [1] K. Zimmermann et al, Gate-‐tunable transmission of quantum Hall edge channels in graphene quantum point contacts. http://arxiv.org/abs/1605.08673 Ce stage pourra se poursuivre par une thèse : Yes (PhD grant funded by a european ERC project) Formation / Compétences : We look for highly motivated students with a strong background in condensed matter physics / quantum physics, and which are willing to address fundamental questions of advanced quantum solid-‐states physics. Période envisagée pour le début du stage : early 2017 Contact : Benjamin Sacépé Institut Néel – CNRS Quantum Nano-‐Electronics and Spectroscopy (QNES) team (http://neel.cnrs.fr/spip.php?article4205) [email protected] Tel: 04 76 88 10 79



51

Visualizing quantum Hall edge channels in Graphene

Quantum Hall effect in two-‐dimensional electron gases has been thoroughly studied for the last decades. Its transport properties rely on the existence of one-‐dimensional conducting channels that propagates along the edge of the sample, each carrying a quantum of conductance (𝑒! ℎ). Despite the large amount of work available on the topic, very little is known about the exact nature and spatial structure of these edge channels. Our group is leading a European research program that aims at performing the first real-‐space visualization of quantum Hall edge channels in graphene by means of scanning tunneling microscopy (STM) and spectroscopy.

The goal of the internship is to perform preliminary STM spectroscopy of the Landau levels

in graphene under high magnetic field. The student will learn state-‐of-‐the-‐art STM instrumentation, and participate in the fabrication of dedicated graphene devices that are suitable for STM measurement. To obtain well resolved Landau levels, high mobility devices will be made by micro-‐transfer of graphene on a hexagonal boron-‐nitride substrate. Measurements will be performed with a newly developed STM head which is cooled down at very low temperature (10mK, dilution fridge) and subjected to a high magnetic field (14T). The STM microscope is capable to work in atomic force microscope (AFM) mode, enabling for large scan area on insulating substrates in order to locate graphene devices. The student will be involved at all levels, from the device fabrication process, to the STM measurements at low temperature and high magnetic field, to the data analysis and interpretation. This study is the first step towards a pioneer investigation of quantum Hall edge channels. The ensuing PhD work will focus on the detailed study of the considerable spatial structure of quantum Hall edge channels, both in the integer and in the fractional quantum Hall regimes. Ce stage pourra se poursuivre par une thèse : Yes (PhD grant funded by a European ERC project) Formation / Compétences : We look for highly motivated students with a strong background in condensed matter physics / quantum physics, and which are willing to work with remarkable instrumentation and address fundamental questions of advanced quantum solid-‐states physics. Période envisagée pour le début du stage : early 2017 Contact : Benjamin Sacépé Institut Néel – CNRS Quantum Nano-‐Electronics and Spectroscopy (QNES) team (http://neel.cnrs.fr/spip.php?article4205) [email protected] Tel: 04 76 88 10 79

Figure | a. Schematic drawing of the STM measurement principle of quantum Hall edge channels. b. The STM spectroscopy gives direct access to the local electronic density-‐of-‐states (DOS) with atomic resolution. The Landau levels will appear as peaks in the DOS. c. 3D sketch of the STM head.

b a c



52

Bio-Activation of Mesoporous Silica Nanoparticles by selective DNA destructuration

Summary : This project aims at synthesizing mesoporous silica nanoparticles (MSNs) containing hosts in the pores and gated using DNA fragments. The cleavage of the DNA fragments by enzymes will allow the opening of the pores, thus the release in solution of the cargo. This will be applied for the detection of DNA-repairing enzymes. Detailed subject: Mesoporous silica nanoparticles (MSNs) constitute a family of nanoparticles (ca 100 nm in diameter) that is widely used for drug delivery owing to the rigidity of the matrix, the high porosity and the possible chemical modification of the surface. Interestingly, the pores (ca 2-3 nm in diameter) can be blocked when nanovalves are grafted, which destroy when a specific stimulus is applied. This has been exemplified with DNA fragments [1]. In this project, we wish to use the same principle for sensing DNA-repairing enzymes [2]. MSNs will be gated with DNA fragments containing lesions. When the repairing enzyme specific to the lesion is present, the pore-gating DNA will be cleaved and the contents of the pores will be expelled, leading to a measurable signal.

This project gathers the expertise of Didier Gasparutto (CEA/INAC/SyMMES) in the synthesis of DNA architectures, and of Xavier Cattoën (Inst Néel) in the synthesis and functionalization of mesoporous silica nanoparticles. [3] [1] Schlossbauer, et al, Angew. Chem. Int. Ed. 2010, 49, 4734 [2] G. Gines, C. Saint-Pierre, D. Gasparutto ; Biosensors & Bioelectronics (2014) 58, 81-84 [3] A. Noureddine, X. Cattoën, M. Wong Chi Man, Nanoscale 2015, 7, 11444–11452 Collaboration: Strong collaboration with Didier Gasparutto (CEA/INAC/SyMMES). This internship may be followed by a PhD thesis. Formation / Compétences : The student should have expertise in chemical synthesis and materials characterization, and a basic knowledge in biochemistry. Période envisagée pour le début du stage : 02/2017 Contact : Cattoën Xavier Institut Néel - CNRS : 04-76-88-10-42 [email protected] Plus d'informations sur : http://neel.cnrs.fr



53

Confined nucleation and growth of molecular nanocrystals for biophotonics and advanced solid-state NMR

General Scope: The shaping of molecular nanocrystals (NCs) in solutions allow to enhance the sensitivity (by several orders of magnitude) and the resolution of a just emerging magnetic resonance spectroscopy called Magic Angle Spinning - Dynamic Nuclear Polarization (MAS-DNP), developed at CEA-INAC. This MAS-DNP spectroscopy will be used to 3D structure determinations (NMR crystallography) of many solid-state systems, which do not easily form large enough crystals (>100 mm) suitable for single crystal X-ray diffraction studies and cannot be easily isotopically enriched in 13C and 15N. Thus, such developments are highly relevant, especially for supramolecular systems, drugs, natural products, self-assembled peptides/nucleotides… etc. On the other hand, we have managed so far the confined nucleation of molecular NCs in sol-gel matrices for biophotonics. Indeed, organic NCs can exhibit intense fluorescence emissions and good photo-stability, which are promising for biological tracers (medical imaging based on fluorescence contrasts). In this case, the NC surface is covered by a silicate shell, which can be functionalized to obtain biocompatible and furtive core-shell nanoparticles in vivo. Research topic and facilities available: The objective will be to control the confined nucleation and growth of molecular NCs in droplets of organic solvents. For that, organic compounds will be dissolved in solvents miscible with water (alcohols, THF, dioxane …). The resulting solutions will be sprayed and suddenly dispersed in water. As water is generally a non-solvent for molecular phases, the corresponding NCs will grow when the solvent droplets will be gradually mixed in water. We recently made a step-forward in the control of this process by producing nanometer-sized crystals of progesterone (around 50 nm in diameter) as shown by scanning electron microscopy in the figure below. The goal is now to produce monodisperse initial droplets to obtain then narrow size distributions of NCs (50-100 nm) by optimizing the nanocrystallization reactor and confined nucleation conditions. The resulting NCs will be characterized by X-ray diffraction, electron microscopies (SEM and TEM), dynamic light scattering, Raman and fluorescence spectroscopies. This research is part of a highly challenging ERC (European Research Council) project on developments of MAS-DNP spectroscopy. Indeed, we believe that our generic process will be widely applicable for molecules exhibiting both a large solubility in solvents miscible with water and a negligible solubility in water, which is the case of a large number of organic compounds. Finally, we will plan to couple this confined nanocrystallization method in solutions to sol-gel chemistry, in order to prepare through a one-step process core-shell nanoparticles: fluorescent NCs surrounded by an amorphous silicate crust for medical imaging applications.

Nanocrystals of progesterone obtained from a methanol solution, sprayed and injected in water.

Possible collaborations and networking: INAC-CEA, CERMAV-Grenoble, CHU-Grenoble … Possible extension as a PhD: Yes Required skills: Solid-state and physical chemistry, basic knowledge on physicochemical and structural characterizations of materials. Starting date: 2017 Contact : Alain Ibanez, Institut Néel, CNRS. Phone: 0476887805 e-mail: [email protected] More information: http://neel.cnrs.fr



54

E-beam electromechanics for quantum nanomechanical engineering General Context: Micro-electromechanical systems have dramatically developed over the past 40 years to become indispensable in modern technology. This success prominently relies on the reduced dimensions of these devices, enabling both high level of integration and ultra-high sensitivity in a variety of applications such as navigation, communication and connected objects. The recent progress in nanotechnology have raised the perspective to further push this approach to nanomechanical systems, with a corresponding size reduction of more than 3 orders of magnitude. However this challenge has so far remained unsuccessful: While being their main strength, the extremely reduced dimensions of nanomechanical systems also represent their Achilles’ heel, making them both extremely difficult to detect and overly sensitive towards external perturbations. The hosts of the proposed project have recently started developing a novel generation of all-integrated hybrid optomechanical components which appear as very promising candidates for tackling the above stated obstacles1. The principle of these devices relies on suspended semiconducting photonic nanowires2 incorporating their own motion readout system, consisting in a quantum dot implanted near their basis. The main ambition is to scale down this concept to nanowires with dimensions in the 10 nm range. Because of its disruptive nature, this research requires to reconsider the whole scientific and technological methodology in order to validate and optimize the proposed approach. In particular, efficient nanomechanical motion readout methods at these scales have been so far missing. Project: The present project proposes to investigate a newly introduced readout scheme enabling ultra-sensitive nanomechanical detection of objects with dimensions down to the nanometer level. The method relies on detecting the fluctuations of the scattered electrons current inside a scanning electron microscope3. The hosts of the project have started to successfully implement this approach for detecting the thermal motion of semiconducting InAs nanowires (cf. Fig. (a)) with a very high sensitivity (see Fig. (b)). This M2 internship will investigate this electromechanical interaction over various semiconducting and conducting materials (GaAs, Si, Carbon nanotubes…) both at ambient and cryogenic temperatures, with the perspective to characterize and stabilize the measurement backaction effects. Possibilities to couple this scheme to cathodoluminescence measurement can be envisioned in a PhD work. References 1 I. Yeo, et al, Nature Nanotechnology 9, 106 (2014) 2 J. Claudon et al. Nature Photonics 4 (3) 174-177 (2010) 3 A. Niguès et al. Nature communications 6, 9104 (2015) Possible collaboration and networking : J. Claudon, J.M. Gérard, M. Hocevar (CEA/INAC), S. Pairis and F. Donatini (Institut Néel), P. Verlot (ILM, Lyon), A. Bachtold (ICFO, Barcelone) This internship can go on to a PhD Required profile : This experimental internship deals with nanomechanics, quantum optics, semi-conductor physics, and electronics Expected start for the internship : First half of 2017 Contact : Jean-Philippe POIZAT, Tél : 04 56 38 71 65 mail : [email protected] More on : http://neel.cnrs.fr/spip.php?rubrique47

Fig. (a) SEM micrograph of InAs nanomechanical wires. (b) Brownian motion spectrum of an InAs nanomechanical wire as obtain using the e-beam nano-elecromechanical measurement technique.



55

Electroless deposition of magnetic nanotubes and core-shell nanowires for a

3D spintronics General Scope: There are proposals to develop a spintronic technology in three dimensions, to lift foreseen limitations of areal density faced by any 2D-based technology such as hard disk drives. Chemical synthesis is the best route to deliver 3D systems such as dense arrays of wires, and joint work between chemists and the spintronic community are emerging. These systems also offer opportunities for new fundamental science of domain walls and spin waves, due to the confined geometry, different topology (circular boundary conditions), and curvature-specific physics [1].

In this context we are pioneering the study of magnetic nanotubes, yet another novel geometry. These are obtained by electroless plating, also widely used in industry for deposition of coatings on various surfaces, including non-

conducting and of high-aspect ratio. It relies on reduction of metallic ions from dissolved salts by a reducing chemical agent. By performing the deposition in nanoporous templates one can deposit large arrays of magnetic nanotubes with diameters down to 100 nm [2]. Various material can be deposited ranging from simple metals to more complex compounds [3] – e.g. NiCoB (see Fig., our own work) [4]. [1] Streubel et al., J. Phys. D: Appl. Phys. 49 , 363001 (2016). [2] Li et al., CrystEngComm 16, 4406 (2014).

[3] Richardson et al., ECS Trans. 64 (31), 39-48 (2015). [4] Schaefer et al., RSC Adv., 6, 70033 (2016)

Research topic and facilities available: The project consists in opening routes to fabricate multi-layered nanotubes, or in other words, core-shell. The motivation is to apply the standard concepts required to implement nanomagnetism and spintronics in a planar technology, to a 3D geometry (eg: ferro/metal/ferro for giant magneto-resistance). This will be done by combining successive electroless plating steps, and/or with Atomic Layer Deposition and/or direct electroplating. This will be done on existing facilities. Structural characterization will be performed using atomic force microscopy, scanning and possibly also transmission electron microscopy, chemical analysis by Energy Dispersive X-ray spectroscopy. Magnetic properties will be evaluated on both arrays of tubes (magnetometry, tubes still in the template) and on isolated tubes dispersed on a flat substrate by focused Kerr (magnetooptics) or magnetic force microscopy. Support of micromagnetic simulation is provided. Possible collaboration and networking: The project is led as a collaboration between INAC/Spintec (O. Fruchart) and Institut Néel. It is part of a larger effort involving international collaboration (TU Darmstadt, FAU Erlangen, Synchrotrons). Possible extension as a PhD: Yes, preferable. Required skills: Physics/Chemistry at bachelor level. A taste for experimental and multidisciplinary work is appreciated. Welcome: physical chemistry, nanomagnetism, characterization techniques Starting date: 1st March 2017 (flexible) Contact: Name: M. Stano / L. Cagnon (Institut Néel – CNRS). O. Fruchart (SPINTEC) E-mails: [email protected] / [email protected] / [email protected]

Fig.: NiCoB tube, from the left: structure+XMCD-PEEM, Transmission electron microscopy

magnetic flux-closure domains



56

Quantum superpositions of causal relations

General context: The study of causal relations has recently gained a lot of interest in the fields of quantum foundations and quantum information. The general objective is to investigate the possible causal relations between events that can exist in the quantum world, and see how they differ from classical relations.

For instance, just like quantum objects can be in a superposition of two incompatible states, one may wonder if there can be superpositions of causal relations: e.g., for the case of 2 events A and B, a situation of the kind “|A causes B> + |B causes A>”.

A framework was recently developed [1] to analyse quantum processes that are incompatible with a definite causal order (i.e., for which one cannot say that A acts before and causes what happens at B, or vice versa). Such processes are called causally non-separable; an example is the quantum switch [2] represented on the right. The framework also allows for processes that generate some new kind of noncausal correlations, which violate so-called causal inequalities; it remains however an open question, whether such processes can indeed be realised in practice. Research project: This project aims at investigating various new practical examples of quantum processes, to test their causal nonseparability and their possible ability to violate causal inequalities. The candidate will resort in particular to the useful analogy between causal nonseparability and entanglement, and between causal inequalities and Bell inequalities [3]. Some of the examples under investigation may not be described in the current form of the framework of [1], which will lead the candidate to propose possible ways to generalize the framework. Various types of “superpositions of causal relations” will be considered, which may involve more than 2 events. [1] O. Oreshkov, F. Costa, and Č. Brukner, Nat. Commun. 3, 1092 (2012). [2] G. Chiribella et al., Phys. Rev. A 88, 022318 (2013); M. Araújo et al., Phys. Rev. Lett. 113, 250402 (2014). [3] M. Araújo et al., New J. Phys. 17, 102001 (2015); C. Branciard et al., New J. Phys. 18, 013008 (2016). Interactions and possible collaborations:

This project will be supervised by Cyril Branciard, and will be conducted in collaboration with the theory group of Alexia Auffèves. The candidate will benefit from interactions with the other group members and from their expertise in a large range of domains (quantum foundations, quantum information, quantum optics, cavity and circuit QED, quantum thermodynamics…). Interactions will also be possible with the group of Prof. Nicolas Gisin at the University of Geneva (Switzerland). This project may be followed by a PhD depending on funding opportunities. Training / Skills: A good knowledge of the formalism of quantum theory and a strong interest in fundamental physics, in particular in quantum foundations and quantum information, are required. Starting date: early 2017 Contact: Branciard Cyril Institut Néel – CNRS. tel: 04 56 38 71 64; e-mail: [email protected] More information on: http://neel.cnrs.fr

The quantum switch: the 2 polarizing beam splitters (PBS) transmit horizontally polarised photons and reflect vertically polarised ones; a |H> photon will thus go to A and then to B, while a |V> photon will go to B and then to A. A photon in a quantum superposition |H>+|V> will thus go to A then B, and B then A, in superposition.



57

New generation of phosphors for eco-efficient LED lighting: Pechini method

General Scope: Lighting by "white LEDs" has become a major challenge for energy saving. However, several problems need to be overcome, the most important are: cost, quality of the white photoluminescence emission and thermal stability. Currently, all devices used, or in development, involve rare earth ions whose main drawbacks are lighting with narrow emission bands with a significant blue component and also their high cost as they are highly strategic elements due to the monopoly of their production by China. At the Institut Néel, we develop a new type of phosphors based on vitreous powders to achieve white LEDs for solid lighting. The innovative character of these aluminum borate phosphors is to produce a broadband luminescence emission throughout the visible spectrum, from color centers (structural defects) in an amorphous matrix. In addition, these phosphors are made of non-toxic and abundant, no rare earth thus making them much less expensive. The project is the pursuit of original work (thesis and patent), which has been initiated in recent years. These phosphors are synthetized by two different “chimie douce” routes: - modified pechini method (polymeric precursors) - sol-gel method (alkoxide precursors); each method leading to a master topic. Research topic and facilities available: the aims of this stage are, firstly: - Understanding the origin of the emitting centers, which are related to structural defects (carbon interstitials...) in order to optimize the luminescence properties. The optimization of the synthesis of these phosphors will be performed by the modified Pechini route, varying chemical factors (nature and stoichiometric ratios of molecular precursors which allow the metal complexation and the polymerization of organic-inorganic network) - change the chemical composition, which is expected to adjust the width of the spectral luminiscent emission in order to improve the light color rendering. A study of the different parameters of thermal treatments (heating rates, the ranges of temperature, controlled atmosphere during treatment), which are at the origin of the presence of emitting centers. Finally, the understanding of the origin and role of emitting centers and the structural characterizations and modeling of the amorphous phase will be implemented by coupled spectroscopic studies: FTIR, UV-Vis spectroscopy, EPR, NMR, X-ray diffraction and X-ray scattering.

Left) Schematic of the process steps: from liquid resin to a luminescent powder. Right) emission spectrum of powder showing a residual peak of the UV incident radiation, non-absorbed by the phosphor, and the broad PL emission band of the phosphor in the whole visible range, between 400 and 800 nm leading to good color coordinates. Possible collaboration and networking: LMGP-Grenoble ; Institut de Recherche Chimie-Paris ; INAC-CEA Grenoble Possible extension as a PhD: Yes Required skills: Solution chemistry, basic knowledge on physicochemical and structural characterizations of material Starting date: Feb. 2017 Contact Name: Salaün Mathieu Institut Néel – CNRS Phone: 04 76 88 10 42 e-mail: [email protected] More information : http://neel.cnrs.fr



58

Mesure de fluctuations de vitesse par anémométrie à fibre optique Cadre général : La physique de la turbulence est étudiée depuis plus d’un siècle mais elle demeure un sujet ouvert. Au sein d’un écoulement turbulent, des tourbillons de tailles différentes interagissent. L’étude de ces interactions entre structures et la compréhension des caractéristiques des très petites échelles constitue un défi majeur qui nécessite la miniaturisation des sondes de mesure. Les capteurs doivent être suffisamment petits pour résoudre les plus petites structures tout en étant robustes et sensibles. Dans cet esprit, nous avons entrepris à l’Institut Néel le développement d’un anémomètre à fibre optique. Les premiers essais ont montré que le principe de fonctionnement de la sonde est valide (voir Figure). Un nouveau prototype est en cours de réalisation. Afin de permettre l’exploitation de la sonde, il est maintenant important de caractériser sa réponse dans un écoulement.

Fig. [à gauche] L’écoulement arrive par la gauche et défléchit la membrane. Son déplacement est mesuré par la fibre optique (d’après Watson et al.) [à droite] Capteur commercial à fibre (FISO).


Nous souhaitons recruter un étudiant en stage afin d’adapter les moyens de tests de l’Institut à l’étude du comportement de la sonde. Pour cela, un écoulement d’air comprimé filtré sera utilisé pour produire un signal de turbulence connu. La sonde sera montée sur une tête goniométrique. L’étudiant devra monter le banc de test à partir de ces différents éléments et l’instrumenter. Il effectuera ensuite une étude systématique de la réponse dynamique de la sonde en fonction de l’angle d’incidence. Le traitement des données devra permettre de caractériser les performances de la sonde. De ce travail dépendra la nouvelle génération de ce type de capteur. Interactions et collaborations éventuelles : L’anémomètre est développé au sein d’une collaboration interne à l’Institut Néel, entre des hydrodynamiciens et des opticiens. L’étudiant sera amené a interagir pleinement avec les différents acteurs de la collaboration. Il devra également collaborer avec les équipes techniques du laboratoire pour les questions de mécanique.

Ce stage pourra se poursuivre par une thèse : Oui Formation / Compétences : Compétences développées: Optique fibrée, Instrumentation, Hydrodynamique & Turbulence, Acquisition & Traitement du signal. Période envisagée pour le début du stage : indifférente Contact : Chabaud Benoit, Institut Néel – CNRS/UGA, [email protected] (contacts alternatifs : Philippe Roche, [email protected] , et Jochen Fick, [email protected] ) Site web : http://hydro.cnrs.me



59

Growth conditions to stabilize polar faces of ferroelectric crystals

General Scope: Periodically poling of KTiOPO4 (KTP) crystals by electric field poling is the way to improve the conversion efficiency by the quasi-phase matching technique [H. Karlsson and F. Laurell, Applied Physics Letters 71, 3474 (1997)]. Electric field poling technique leads to periodically poled crystals of limited thickness that is detrimental to obtain high power application. A way to getting around this limitation consist in the growth, from high temperature solutions, onto polar faces of periodically poled KTiOPO4 (PPKTP) thin slabs obtained by electric field poling [A. Peña, et al., Optical Materials Express 1, 185 (2011) and Journal of Crystal Growth 360, 52 (2012)]. Nevertheless, this growth process have to take into account kinetic and thermodynamic considerations in order to propagate the grating periodicity of the initial seed to the as grown layer.

Research topic and facilities available: The research project will be focused in doing several growth experiments onto single domain KTP slabs in order to determine the stability of {001} polar faces. The first objective of the project is to find the experimental conditions to be able to stabilize both non-equivalent polar faces, (001) and (00-1). The second one is growing these faces at the same growth rate to be able to grow thick PPKTP crystals to be used in high power optical devices. The growth devices are available in the technical services (pôle Cristaux Massifs of MCBT department) and the SEM and AFM in the technical services (pôle Optique et microscopies of PLUM department) of Institut Néel.

Possible collaboration and networking: The master 2 stage is going to be under the supervison of Alexandra Peña Revellez(CR1, OPTIMA research team) and in close interaction with Bertrand Ménaert (IRHC, pôle Cristaux Massifs), and Benoît Boulanger (PRCE1, OPTIMA research team). Collaborations, Jérôme Debray (IE2, pôle Cristaux Massif) will also be important. Possible extension as a PhD: The internship could move on a PhD if financial support is found. Required skills: Materials science Skills in crystal growth will be appreciate Starting date: March 2017 Contact: Name: Alexandra Peña Revellez Institut Néel - CNRS Phone: (33) 4 76 88 79 41 e-mail: [email protected] (33) 4 76 88 78 03 [email protected] More information: http://neel.cnrs.fr



60

Growth of the chiral ferromagnet LiFe5O8 by high temperature flux method

General Scope: Chiral magnetic compounds, forming chiral structures both crystallographically and magnetically, has been the subject of considerable interest lately due to unique magnetic properties such as magneto-chiral dichroism (MChD) and nonreciprocal magnon propagation [Y. Iguchi, et al., Phys. Rev. B 92, 184419 (2015)]. Such phenomena can be cancelled by racemic twin crystals, so it is important to find the experimental conditions to grow homo-chiral single crystals. The chiral ferromagnet LiFe5O8 is attractive because it shows a high magnetic transition temperature at 655 °C [E. Rezlescu, et al., Cryst. Res. Technol. 31, 739 (1996)]. It undergoes a structural phase transition at around 720 °C from a high temperature centro-symmetric structure (Fd-3m space group) to a chiral one (P4132 or P4332 space group).

Research topic and facilities available: The growth of homochiral crystals LiFe5O8 is a big challenge. Indeed, the fluxes tried so far does not allow to grow the crystal below their phase transition temperature of 720°C. Recently, during a collaboration between Hiroshima University and Institut Néel, a promising new flux system that will allow growing this crystal below its phase transition temperature has been identified. The main objective during the internship is the growth of LiFe5O8 crystals in the new flux and determine whether they are homochiral or not. The growth devices are available in the technical services (pôle Cristaux Massifs of MCBT department) and the X-ray facilities in the technical services (pôle X’Press of PLUM department) of Institut Néel.

Possible collaboration and networking: The master 2 stage is going to be under the supervison of Alexandra Peña Revellez(CR1, OPTIMA research team) and in close interaction with Bertrand Ménaert (IRHC, pôle Cristaux Massifs) and Isabelle Gautier-Luneau (PR1, OPTIMA research team). Collaborations, Olivier Leynaud (IR2, pôle X’Press) will also be important. Possible extension as a PhD: The internship could move on a PhD if financial support is found. Required skills: Materials science Skills in crystal growth will be appreciate Starting date: March 2017 Contact: Name: Alexandra Peña Revellez Institut Néel - CNRS Phone: (33) 4 76 88 79 41 e-mail: [email protected] (33) 4 76 88 78 03 [email protected] More information: http://neel.cnrs.fr



61

Turbulence Quantique : étude expérimentale

Cadre général : En dessous de 2,17 K, l’hélium liquide acquiert des propriétés superfluides : il peut s’écouler sans viscosité et la vorticité de son champ de vitesse devient quantifiée. On s’attend donc à ce que sa turbulence, appelée « Turbulence Quantique », diffère de la turbulence « classique ».

D’après plusieurs études récentes, il semble que la principale différence soit concentrée au niveau des plus petits tourbillons présents dans ces 2 types de turbulence. En effet, en l’absence d’une dissipation efficace, on s’attend à ce que les tourbillons superfluides s’accumulent aux petites échelles de l’écoulement.

L’objectif est de détecter et comprendre cette différence, grâce à un détecteur conçu à cet effet.

Sujet, moyens disponibles : Dans le cadre du stage et de la thèse, l’étudiant développera un capteur de vortex miniature (<100 µm) en tirant profit de l’environnement grenoblois en nano-technologies (nanofab, PTA/Minatec). Ce capteur sera ensuite exploité dans nos différents écoulements d’hélium liquide, soit superfluide soit classique, afin de comparer les propriétés physiques des deux types de turbulence. L’un de ces écoulements sera la soufflerie TOUPIE, spécialement construite pour répondre à cet objectif, et qui bien vient de bénéficier d’un upgrade pour atteindre des températures approchant 1K, un record pour une soufflerie cryogénique de grande taille.

Interactions et collaborations éventuelles : Le projet s’inscrit dans le cadre du projet inter-laboratoires (CEA/CNRS/ENSL/INP/UGA) SHREK (financement ANR), centré sur une cellule d’étude de la turbulence superfluide de très grande taille (env. 1m3). Des expériences seront aussi conçues pour cette cellule.

Ce stage pourra se poursuivre par une thèse : Oui Formation / Compétences développés : Hydrodynamique & Turbulence quantique, Physique des basses températures & Cryogénie, Nanotechnologie & Technique de microfabrication, Acquisition & Traitement du signal, Instrumentation & Mesures bas bruit Période envisagée pour le début du stage : indifférente Contact : Roche Philippe, Institut Néel – CNRS/UGA [email protected] (04 76 88 11 52) http://hydro.cnrs.me

T

Tourbillons superfluides (simulation)

Tube de Pitot miniaturisé permettant la mesure de

fluctuations de vitesse superfluide



62

Dielectric properties of the Cooper-pair insulator

When a superconducting disordered thin film is subjected to an increase of disorder or to a strong magnetic field (B) it can undergo a transition to an insulating state. This transition is a quantum phase transition (driven by a change of a parameter of the Hamiltonian at T=0) between two antinomic ground states, the superconducting and insulating ground states. In recent years the insulator drew significant interest due to the body of experimental work that indicates that charge carriers in it are localized Cooper-pairs [1]. It is thus considered as a unique playground to investigate an interacting, many-body quantum system of localized Cooper-pairs in a disordered potential.

The transition to the so-called Cooper-pair insulator is easily tuned in experiments by applying a strong perpendicular magnetic field. The above figure shows a typical B-tuned transition from superconductor at B=0 to the Cooper-pair insulator at finite B with a diverging magnetoresistance resistance peak at the lowest temperature. The nature of the insulator in this magnetoresistance peak is the focus of our current research activities.

The goal of this Master project is to perform innovative high frequency measurements of the dielectric properties of the Cooper-pair insulator using state-of-the-art superconducting micro-wave resonators. The underlying physics to unveil is a possible signature of a new transition to a new insulating state with strictly zero conductivity at finite temperature (called many-body localized state) [2]. The student will participate in the design of RF superconducting resonators that serve to probe of the dielectric constant. She/He will prepare and characterize superconducting samples by magneto-transport measurements (down to 10mK and 18T), and start the first high frequency measurements of the dielectric constant. These initial measurements will give crucial information about the role of Coulomb interaction in the superconductor insulator transition.

[1] B. Sacépé et al. Localization of preformed Cooper pairs in disordered superconductors, Nature Physics 7, 132 (2011). http://arxiv.org/abs/1012.3630 [2] M. Ovadia et al. Evidence for a Finite Temperature Insulator. Nature Scientific Reports 5:13503 (2015) http://www.nature.com/articles/srep13503 Interactions et collaborations éventuelles : Superconducting resonators : Alessandro Monfardini, HELFA team. Landau Institute for Theoretical Physics (Moscow). Weizmann Institute of Science. Ce stage pourra se poursuivre par une thèse : Yes Formation / Compétences : We look for highly motivated students with a strong background in condensed matter physics / quantum physics, and which are willing address fundamental questions of advanced solid-states physics. Période envisagée pour le début du stage : early 2017 Contact : Benjamin Sacépé, Institut Néel – CNRS Quantum Nano-Electronics and Spectroscopy (QNES) team (http://neel.cnrs.fr/spip.php?rubrique49) [email protected] Tel: 04 76 88 10 79



63

Synthesis of Chiral Crystals for magnetism, spintronic and Nonlinear Optics

Cadre général : This subject aims at synthesising and then studying the growth of two chiral compounds in order to obtain large, homochiral crystals. The two selected compounds are quite similar : CsCuCl3 and CsGeCl3. The first one is a chiral magnet with exotic properties of great interest for science (nonreciprocal magnon propagation,…) and applications (spintronic) that are studied by Japanese collaborators (Pr. K. Inoue and Y. Kousaka, Hiroshima University). The second commpound has recently been shown as a potential non linear optical frequency converter in the visible to the far infra-red (0.3-20µm) which is the main interest of part of our group at Institut Néel. Yet no single crystal have been grown and no real non linear study have been performed on this compound. This work will thus involve first the synthesis of the compounds and then the study of theire crystal growth in a dedicated growth reactor. Once crystals of a few mm are obtained, conditions favoring an enantiomorphic selective crystallization will be studied by adapting condition employed in Viedma ripening. Sujet exact, moyens disponibles : In order to grow large homo-chiral CsCuCl3 single crystals we propose to use our rapid growth system developed and patented by Institut Néel It proved remarkably efficient at growing large (5-7cm) single crystals of high purity and high quality of KH2PO4 and the K(D1-xHx)2PO4 solid solution used as case studies (Figure 1). The first exploratory growth runs of CsCuCl3 with this system proved very encouraging. The determination of the optimal growth conditions (solvent, temperature, growth rates, …) should now be undertaken in order to provide to the physical studies the large homo-chiral single crystals they require. In the case of CsGeCl3, two synthesis routes exist in the literature; both are done at moderate temperatures (<100°C) and employ standard chemicals. Yet the exact conditions leading to the highest synthesis yields of CsGeCl3 should be explored. The similarity with the previous compound will allow to transpose almost directly all the growth conditions to this new compound. Finally, ways to influence the chirality of the crystals synthesized have recently been identified (called Viedma ripening) by using grinding or thermal cycling, our growth method being compatible with both, their introduction in the process will be tested to determine their impact on the homochirality of the grown crystals. Possible collaboration and networking : Possible extension as a PhD : No Required skills : Solution chemistry, knowledge in physicochemical and structural characterizations of materials Période envisagée pour le début du stage : Contact : ZACCARO Julien Institut Néel - CNRS : phone : 04 76 88 7804 email : [email protected] More info sur : http://neel.cnrs.fr

Figure 1 Large (5 cm) KH2PO4 high purity and high quality single crystal grown at about 10 mm/day by the method patented by Institut Néel



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Quantum simulation in circuit-QED Scientific Context: While the universal quantum computer is a very promising but very demanding route towards quantum computation, quantum simulators appear as a faster approach to quantum speedup. Based on an idea initially suggested by R. Feynman, a quantum simulator is a machine dedicated to a given class of physical problems (e.g. quantum magnetism, fermionic or bosonic Hubbard models...). The required building blocks (quantum bits) as well as the control electronics are similar to the one of the universal quantum computer but since universality is not required, the overhead developments are less stringent. As such, they are considered as the first architecture, which will allow tackling problems intractable with classical computers.

We are developing quantum simulators based on superconducting quantum bits coupled to microwave photons. This architecture has been dubbed circuit Quantum ElectroDynamics (circuit-QED), for a recent review you can look at [1]. The quantum simulator we demonstrated recently (see figure) aims at unraveling quantum impurity problems, which are integral to the understanding of strongly correlated materials or high-Tc superconductors [2]. [1] Devoret, M. H., & Schoelkopf, R. J. Science, 339(6124), 1169–1174 (2013). [2] Snyman, I., & Florens, S. Physical Review B, 92(8), 085131 (2015). Description, available means: Our team has a strong experience in nanofabrication, microwave electronics and cryogenic equipment. The student will first design and fabricate a new generation of our quantum simulator in the clean room of the Neel Institute (Nanofab). She/He will then carry out the measurements of the device at very low temperature (20mK), using one of the three fully equipped dilution refrigerators of the team. The “Agence Nationale pour la Recherche” (National French Funding Agency) recently funded this project. Interactions and collaborations: Our team is part of several national and international networks. For this specific project we are collaborating closely with the group of Serge Florens at the Néel Institute and with the group of Izak Snyman at the University of Witwatersrand in Johannesburg, South Africa. Education / Profile: Master 2 or equivalent. We are seeking motivated students who want to take part to a state of the art experiment and put some efforts in the theoretical understanding of quantum simulation using superconducting quantum circuit. This internship can be pursued toward a PhD Start Period: Flexible Contact : ROCH Nicolas Institut Néel - CNRS : phone: +33 4 56 38 71 77 email: [email protected] Plus d'informations sur : http://neel.cnrs.fr & http://perso.neel.cnrs.fr/nicolas.roch

a. Overview of the first generation of our quantum simulator (Optical microscope image). It is made of a superconducting quantum bit (red rectangle) coupled to superconducting meta-materials (blue rectangle). b. Detail of the meta-material, which is made of 5000 Josephson junctions (SEM image). c. Josephson junction forming the quantum bit (SEM image).

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Nouveaux matériaux magnétiques fonctionnels Les matériaux magnétiques sont à la base de nombreuses applications de hautes technologies que ce soit dans le domaine du stockage de l’information, de l’électrotechnique (moteurs, détecteur, actionneurs) ou de l’automobile (véhicules électriques ou hybrides). Ainsi toute amélioration de ces matériaux se traduit directement par un gain de performance ou peut aussi ouvrir de nouvelles applications. Récemment cela a aussi permis de mettre à jour de nouveaux matériaux présentant une forte magnétorésistance, ou même des propriétés magnétocaloriques exceptionnelles ouvrant ainsi de nouvelles fonctions (stockage d’informations, réfrigération magnétique…). Les recherches se concentrent sur l’étude de composés associant au moins deux éléments aux propriétés complémentaires : métal de transition (Fe, Co) et un élément de terre rare. Cela s’est avéré fructueux pour les matériaux magnétiques durs (aimants) et plus récemment pour les matériaux magnétocaloriques en conduisant à des matériaux aux propriétés inégalées. Cette démarche doit être approfondie pour en découvrir de nouveaux, optimiser les propriétés physiques en général et magnétiques en particulier. Sujet : Le stage à caractère expérimental comprendra l’étude de nouveaux composés que nous avons mis à jour et la détermination de leurs propriétés magnétiques macroscopiques ainsi que l’analyse de leurs propriétés structurales. Les propriétés physiques essentiellement seront déterminées par mesures magnétiques variées : - mesures d’aimantation en champ fort, - susceptibilité alternative, - analyse thermomagnétique, - chaleur spécifique. Des mesures diverses (aimantation, résistivité…) seront effectuées à basses températures (300 à 2K). La compréhension des propriétés physiques originales de ces nouveaux composés nécessite la connaissance de leur structure. La diffraction des rayons X sera aussi mise en œuvre en complément. L’objectif de ce travail est de mettre à jour et comprendre les mécanismes qui régissent les propriétés de ces matériaux prometteurs. Interactions et collaborations : Ces études à l’Institut Néel s’appuieront sur et plusieurs collaborations et internationales existantes (mesures sous pression, études spectroscopiques) au niveau européen (Allemagne, République Tchèque…) et plus largement mondial (Australie, Canada). Ce stage pourra se poursuivre par une thèse, il n’est pas limité à un niveau M2R. En effet ce sujet est au cœur des préoccupations de notre équipe et a vocation à se poursuivre par un doctorat. Dans le cadre d’un doctorat nous mènerons aussi des études sur les grands instruments n tirnat profit de la complémentarité entre rayons X et neutrons. Formation / Compétences nécessaires : M2R ou Ingénieur en Physique des Matériaux. Ce sujet à caractère expérimental sera l’occasion d’approfondir les connaissances en magnétisme, physique du solide et cristallographie. Période envisagée pour le début du stage : février ou mars 2017 Contact : ISNARD Olivier Département PLUM Institut Néel - CNRS : tél 04 76 88 11 46 email [email protected] Plus d'informations sur : http://neel.cnrs.fr



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Investigation of magnetization processes in R-M intermetallic compounds Introduction : The R-M phases based on rare-earth (R) and transition metals (M) are fascinating materials from both applied and fundamental viewpoints. Indeed, R-M have led to the first modern magnets like Sm-Co (SmCo5 and Sm2Co17 type) and latter to the high performance Nd-Fe-B magnets. Other examples are the (Dy,Tb)Fe2 type Terfenol ® alloys which are by far the best magnetostrictive materials to date and are widely used in sensors and actuators leading to many applications (Sonar). Other R-M alloys have also contributed to the development of various techniques such as magneto-optic recording on thin films (Gd-Co). Some compounds are now also considered for new applications such as spintronic devices (Gd-Co), magnetic refrigeration using magnetocaloric materials (LaFeSi, RCo2..). The R-M compounds are however complex materials and need fundamental studies to master their magnetic properties and optimize their performances. Indeed, they are combining two types of magnetism, the localized magnetic moment originating from the inner 4f electronic shells of the R element with the delocalized magnetic moments carried by the itinerant 3d electrons of the M transition metals. Depending upon the atomic concentration one can thus play with different origin of the magnetization. From a fundamental point of view, the R-M compounds are ideal systems to probe solid state magnetism since they are presenting a wide range of unusual magnetic behaviour. Research to be carried out : Among the interesting magnetization process that attracted our attention, we can cite magnetization reversal in hard magnetic materials exhibiting promising magnetic properties for permanent magnet applications. We also recently discovered the occurence of ultrasharp magnetization behaviour in LaFe12B6 see Figure. This manifest itself by unexpected giant metamagnetic transitions consisting of a succession of extremely sharp magnetization steps separated by plateaus. This behavior has been found at low temperature in LaFe12B6. This unprecedent behaviour for a purely 3d itinerant electron system needs to be further investigated since it presents many remarkable properties. For instance, under certain combinations of the external parameters (temperature and magnetic field), the time dependence of the magnetization displays an unusual step-like feature. However, the origin

and the underlying mechanism involved in such unusual magnetization process have to be clarified. The internship will include synthesis of polycrystalline samples, measurements of their physical properties (structural and magnetic) and analysis of the observed behavior. This will be done in close interaction with the researchers.

Ongoing collaborations : In the frame of this research work, different collaborations are already established in particular with the Institute Laue Langevin, as well as Czech collaborators specialists of magnetic measurements at high pressure. This will be an added value to the project. This internship is aimed to be followed by a Ph. Thesis Formation / skills : Master 2 in Solid State Physics or Nanophysics or Engineer in Materials sciences Starting period foreseen : February or march 2017 Contact : Pr. Olivier ISNARD, Département PLUM Institut Néel - CNRS : tél 04 76 88 11 46 email [email protected] see also : http://neel.cnrs.fr

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Development of new magnetic actuators for biology applications at the cellular scale

Cadre général : The understanding of biological processes at the cellular level requires new tools to study the effect of localized stimuli on single cells. The interaction between a magnetic field and a magnetic micro-object (micro/nano-particle, micro-pillar) can remotely produce forces and strain on isolated cells which are in comparable intensity to biologically relevant forces. For this purpose, it is necessary to design new magnetic flux sources, at the micron scale, based on various materials to address some of the latest challenges of cellular biology. In our group, we have developed multiple approaches to produce micro-sources of magnetic flux[1,2] which were already used for cell sorting and mechanotransduction studies [3,4]. The next step is to control forces in the piconewton range and local deformation in the micron range. To be statistically relevant, such experiments need to be repeated many times, and the ideal device is a highly parallel system where an array of single cells is collectively excited by an array of micro-magnets. [1]Dumas-Bouchiat et al. Applied Physics Letters 96,(2010): 102511 [2]Dempsey et al. Applied Physics Letters 104, (2014): 262401 [3]Osman et al. Biomicrofluidics 7,(2013): 54115 [4]Brunet et al. Nature Communications 4 (2013): 2821 Sujet exact, moyens disponibles : Two different systems will be considered. In the first case, micro-magnets (fig.1) that can be moved in an external magnetic field, so as to induce mechanical stress on single cells, will be developed. In the second case, stationary micro-magnets will be developed to apply a very local force on a single cell, through the attraction of magnetic nanoparticles either embedded in or attached to the cell membrane. The student will take part in the design, fabrication, characterization and testing of the micro-magnets. The design will be complemented with numerical simulations in order to optimize the dimensioning of the devices and the choice of material. Micro-fabrication will be carried out with clean room based lithography/etching/deposition techniques (Nanofab-Neel and PTA-Minatec). After characterization and testing, the micro-magnets will be integrated into systems for biology studies. Interactions et collaborations éventuelles : Interaction with biologists and biophysicists at LIPhy (Grenoble) and Institut Curie (Paris) for testing of the developed devices. Ce stage pourra se poursuivre par une thèse. Formation / Compétences : The candidate must have good experimental skills and a master2 in physics, material science or biophysics Période envisagée pour le début du stage : Spring 2017 Contact : Devillers Thibaut Institut Néel - CNRS : tél +33 (0)476887435 e-mail : [email protected] Plus d'informations sur : http://neel.cnrs.fr

Figure 8 : SEM of magnetic micro-pillars produced by Deep reactive ion etching followed by Fe deposition



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Fig. 1 Schema of spin filtering (J S Moodera et al.,J. Phys.: Condens. Matter 19 (2007) 165202

Fig. 2 SXRD measurement showing the epitaxial growth of CoFe2O4(100)/Ag(100)

Growth of ferrimagnetic spinels for spin-filtering General Scope : Spin based electronics take advantage of both the electron charge and spin in solid-state systems. A crucial component in applications is the magnetic tunnel junction (MTJ), where two magnetic layers sandwich a non-magnetic one. Its conductance depend on the relative spin orientation of the two electrodes. An alternative way for generating spin-polarized currents is based on MTJ with magnetic barrier materials, which results in spin dependent tunneling probabilities (Fig. 1). Efficient spin-filtering has been demonstrated for ferromagnetic insulators such as EuS and EuO, which show low transition temperatures. Spinel ferrites like CoFe2O4 are promising candidates for room-temperature spin filtering. Spin based electronics take advantage of both the electron charge and spin in solid-state systems. A crucial component in applications is the magnetic tunnel junction (MTJ), where two magnetic layers sandwich a non-magnetic one. Its conductance depend on the relative spin orientation of the two electrodes. An alternative way for generating spin-polarized currents is based on MTJ with magnetic barrier materials, which results in spin dependent tunneling probabilities (Fig. 1). Efficient spin-filtering has been demonstrated for ferromagnetic insulators such as EuS and EuO, which show low transition temperatures. Spinel ferrites like CoFe2O4 are promising candidates for room-temperature spin filtering. Research topic and facilities available: We have recently grown epitaxial CoFe2O4(100) films of nanometric thickness on a Ag(100) substrate and investigated their structure by in-situ surface x-ray diffraction (SXRD, fig. 2). We need now to optimize the surface structure and morphology, a crucial step to get the desired properties. A magnetic electrode - in our case consisting of magnetite - will be next grown on top to realize a spin-filtering device. This electrode need to be magnetically decoupled, which can be realized by the insertion of a magnesium oxide ultrathin layer in-between. Resuming, during the internship we will study the growth of a Fe3O4/MgO/CoFe2O4/Ag(100) three-layer.

The lattice constants of each layer of this all oxide system match very-well, which should result in a model epitaxial MTJ. The samples will be elaborated using a MBE system equipped with several thermal evaporation sources and the morphology and epitaxy will be studied in-situ by scanning tunneling microscopy (STM) and low energy electron diffraction (LEED), and ex-situ by XRD. A first characterization of the electronic properties will be performed with scanning tunneling spectroscopy (STS). Magnetic properties will be further characterized using x-ray magnetic circular dichroism at the absorption Co and Fe L edges. This second part however is beyond the scope of the master and can be included in a PhD subject. Possible collaboration and networking: SIN team (Néel Institut), X. Torrelles, ICMAB (Spain) Possible extension as a PhD: Yes Required skills: A good background in condensed matter physics and a strong motivation for experimental work are required Starting date: March, 2017 Contact: Maurizio De Santis Institut Néel - CNRS Phone:04 76 88 74 13 e-mail: [email protected] More information: http://neel.cnrs.fr



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Scanning Josephson Tunneling Microscopy: visualizing bound states in Superconductors

The ability of electrons to tunnel between two conductors is extremely sensitive to both distance and density of states. This has made scanning tunneling microscopy/spectroscopy (STM/STS) an extremely sensitive and versatile tool to visualize atomic scale topographic features and variations in the local density of states. When both conductors (that is, tip and sample) are superconducting, the tunneling of Cooper pairs can be even more sensitive to the sample’s electronic properties, an effect which has recently led to exciting discoveries. The target of this Master/PhD project is to implement the Scanning Josephson Tunneling Microscopy (SJTM) technique in our laboratory. Nanometer scale scatterers (single atom, molecule, quantum dot) can interact with the superconducting condensate via potential scattering and/or magnetic exchange coupling. This can lead to bound states at energies below the superconducting gap with

peculiar spatial and spectral properties. Using SJTM we will investigate the interplay of superconductivity to with such local perturbations, as a function of magnetic field and an external gate potential.

Figure 1: Local density of states map around magnetic adatom on Pb and sketch of STM experiment using superconducting tip.

This project will be carried out using a low temperature STM operating at 100 mK, at Institut Néel [1]. Part of the experiments will be performed in the group of K. Franke (Berlin), in a low temperature STM with complementary capabilities [2]. The student’s work will encompass:

- Clean-room nanofabrication (substrates for impurity gate control, superconducting tips) - Ultra-low noise electronics development (current bias to a high impedance junction) - Low temperature, scanning probe and ultra-high vacuum techniques - Theoretical analysis and interpretation

[1] Charge Puddles in Graphene Near the Dirac Point, S. Samaddar, I. Yudhistira, S. Adam, H. Courtois, and C.B. Winkelmann, Phys. Rev. Lett. 116, 126804 (2016). [2] Magnetic anisotropy in Shiba bound states across a quantum phase transition, N. Hatter, B.W. Heinrich, M. Ruby, J.I. Pascual, K.J. Franke, Nature Comm. 6, 8988 (2015). Interactions et collaborations éventuelles : This project will be carried out in collaboration with the group of K. Franke (Berlin). Experiments will be carried out at both locations. At both locations, analysis and interpretation will benefit from strong local theoretical support (D. Basko / Grenoble, F. von Oppen / Berlin). Ce stage pourra se poursuivre par une thèse (ou ce sujet est limité à un stage M2...). Yes Formation / Compétences : Master in Physics Période envisagée pour le début du stage : beginning of 2017 Contact : Winkelmann Clemens / Courtois Hervé Institut Néel - CNRS : 04 76 88 78 36 [email protected] Plus d'informations sur : http://neel.cnrs.fr/spip.php?rubrique49



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Model hard-soft magnetic nanocomposites

Cadre général : Rare earth - transition metal (RE-TM) magnets play an important and growing role in the clean energy sector, being key components of hybrid electric vehicles and gearless wind turbines. The growth in the room temperature energy product of permanent magnets, which doubled in value every 18 years in the last century, has been practically stagnant over the last 20 years. This is because no new magnetic phases having intrinsic properties better than those of today’s best material, Nd2Fe14B, have been discovered. Kneller and Hawig proposed an elegant approach to further increase the energy product of magnets using known materials, by producing a nano-structured composite material that combines a hard magnetic phase exchange coupled to a high magnetisation soft phase [1]. Such nanocomposites would also reduce the overall RE content of the magnet, which is very important in light of recent concerns with the sourcing and pricing of RE elements. While much effort has gone into producing hard/soft nanocomposites, no studies reported significantly enhanced energy products because of insufficient control over the nanostructure, in particular the size of the soft phase grains and the crystallographic texture of the hard phase grains.

Sujet exact, moyens disponibles : The student will develop and study model hard/soft nanocomposites with an unprecedented level of control over the sample nanostructure. Nano-lithography will be used to fabricate arrays of FeCo nano-rods of controlled size, shape, position and overall surface content. Sputtering will be used to fabricate a highly coercive NdFeB hard magnetic matrix [2]. Structural characterization will be carried out using X-Ray diffraction, Atomic Force Microscopy, Scanning and Transmission Electron Microscopy.

Figure 1 : SEM / MFM images of FeCo nano-lithographically patterned rods.

Magnetic characterization will be carried out using VSM-SQUID magnetometry, Magnetic Force Microscopy under field, Scanning Magneto-Optic magnetometry and possibly X-ray Magnetic Circular Dichroism. [1] E. F. Kneller, & R. Hawig, IEEE Trans. Magn. 27(1991) 3588 [2] N.M. Dempsey, T.G. Woodcock, et al., Acta. Mat. 61 (2013) 4920 Interactions et collaborations éventuelles : The student will work closely with a post-doc at Institut Néel on sample preparation and characterisation, in the framework of an ANR project involving three other labs (SPCTS-Limoges, ILM-Lyon and the ESRF). Ce stage pourra se poursuivre par une thèse. Formation / Compétences : The candidate must have good experimental skills and a master2 in physics or material science. Période envisagée pour le début du stage : Spring 2017 Contact : DEMPSEY Nora Institut Néel - CNRS : tél +33 (0)476887435 e-mail : [email protected] Plus d'informations sur : http://neel.cnrs.fr



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Plasmonic response of copper nanoparticles during their growth on TiO2

General Scope: Noble metal Au, Ag and Cu nanoparticles (NPs) have the unique ability to absorb visible (ViS) part of the electromagnetic field due to the resonance with a collective oscillation of their conduction electrons (fig. 1). This excitation is called localized surface plasmon resonances (LSPR). It has been very recently shown that LSPR can strongly enhance the catalytic activity under visible-light and act as a photocatalyst. The involved mechanisms are under debate. The understanding of the plasmonic assisted photocatalysis is an important issue since it opens a new way allowing to overcome the limit of conventional Semi-Conductor mainly active in ultra-violet (UV). In this context of photocatalysis, Cu is of a particular interest because of its chemical activity, it is also the most abundant and the cheapest noble metals.

Research topic and facilities available: The internship will be devoted to the study of the plasmonic response of copper nanoparticles during their growth on a TiO2 crystal. The aim is to correlate the structural properties with the optical ones. The setup which will be used is shown on the picture (2). The nanoparticles are grown by molecular beam epitaxy in an ultra-high vacuum chamber. Their optical response are measured by Surface Differential Reflectivity Spectroscopy (SRDS). It consists to measure the relative variation of the reflectance under UV-Vis light during copper deposition compared to the bare substrate (3).

Possible collaboration and networking: INSP paris, IRCE Lyon Possible extension as a PhD: oui Required skills: This subject is intended has students having physicist's training and/or in nanosciences Starting date: avril 2017

Contact: Name: SAINT-LAGER Marie-Claire Institut Néel - CNRS Phone:04 76 88 74 15 e-mail: [email protected] More information: http://neel.cnrs.fr



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Mixed order phase transition Cadre général : The general framework is the lattice statistical mechanics, more precisely the study of phase transitions. Sujet exact, moyens disponibles : The purpose of the internship is to study a lattice model recently proposed by D. Mukamel. This model has the property to have both a jump in the magnetization and a diverging correlation length. This is a very peculiar situation since usually a jump in the order parameter is a landmark of first order transition, while a diverging correlation length characterizes second order phase transition. This result is an exact result, free of any approximation. The goal of this work is to study the finite size effect in this system. Firstly it will be necessary to understand the result shown in the above mentioned paper, then to get some intuition to determine the size effect for such systems. A part of the work being numerical, the computing power of the Institut Néel will be used. Interactions et collaborations éventuelles : This work is a part of an ongoing collaboration with hungarian physicists from Budapest (Hungary) Ce stage pourra se poursuivre par une thèse (ou ce sujet est limité à un stage M2...). A priori no. Formation / Compétences : Beside knowing the first results in lattice statistical physics (eg Ising model) Interest and skills in computational physics is needed for this internship. Période envisagée pour le début du stage : anytime Contact : Anglès d’Auriac Institut Néel - CNRS : 04 76 88 78 42 mel [email protected] Plus d'informations sur : http://neel.cnrs.fr



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Listening to the noise of a four-terminal Josephson junction

Introduction : In the Josephson effect, a nondissipative supercurrent flows through a phase-biased weak link between two superconductors. The Josephson effect is one of the most important building block of quantum nanoelectronic circuits. In our group, we study more specifically more complex Josephson junctions with three or four terminals (see the figure for a three-terminal Josephson junction). A recent experiment [1] provided evidence for quantum fluctuations of the current (e.g.

current noise) in a three-terminal Josephson junction. The internship will be about calculations of the current noise in a four-terminal Josephson junction consisting of three superconductors and one normal lead. Those four-terminal Josephson junctions may offer the opportunity to provide information on the number of Cooper pairs participating to a single current-carrying quantum process (the so-called effective charge). [1] Y. Cohen, Y. Ronen, J.-H. Kang, M. Heiblum, D. Feinberg, R. Mélin and H. Shtrikman, submitted to Science, https://arxiv.org/abs/1606.08436 Proposed work-program : The noise in those four-terminal junctions is expected to originate from the exchange between pairs (from the superconducting leads) and normal electrons (in the normal leads). It is expected that the student will provide information on the interest of making those experiments in the next years. The intership will consist of analytical Green’s function calculations for the average current and noise in a four-terminal Josephson junction. Interactions and possible collaborations : This project is within the framework of national and international collaborations that we have been developping over the last years. It is expected that the student should interact on a daily basis with the other members of our group in Grenoble (Serge Florens and Denis Feinberg who is developping Nazarov’s circuit theory calculations for similar set-ups), as well as with our close collaborator Benoît Douçot in Jussieu. The student is expected to visit the experiment of François Lefloch in CEA-Grenoble. This work is also within an on-going collaboration with the experimental group of Moty Heiblum at the Weizmann Institute in Israël. Both of those experiments can measure (in different regimes) the noise which will be calculated during the internship. The intership can be followed by a PhD thesis. Required skills : It is expected that the student should master well the main ideas of his M2 advanced course on Quantum Mechanics. Period for the internship : Anytime during academic year 2016-2017 Contact : Régis Mélin Institut Néel - CNRS 04-76-88-11-88, [email protected]



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Systèmes Hybrides Spin-Nanorésonateurs mécaniques

Le refroidissement et l’observation d’un oscillateur mécanique macroscopique dans son état quantique fondamental, réalisé en 2010-2011 dans plusieurs laboratoires, permet maintenant d’envisager la génération d’états mécaniques non-classiques. Pour ce faire une stratégie consiste à coupler ce résonateur mécanique ultrafroid à un autre système quantique, un qubit, dans le but de transférer sa nature quantique à l’oscillateur. Ce faisant on réalise un système hybride mécanique couplant les deux briques de bases de la mécanique quantique [1,2].

Le groupe de recherche Nano-optomécanique quantique hybride de l’Institut Néel explore une voie dans laquelle des nanofils de carbure de silicium sont couplés au spin électronique d’un centre coloré du diamant, le centre NV (pour Nitrogen-Vacancy). Une première expérience de principe [1] a permis de développer ce système hybride spin-oscillateur: un centre coloré hébergé dans un nanocrystal de 50 nm de diamètre a été déposé à l’extrémité d’un nanofil de SiC. En immergeant le système dans un très fort gradient de champ magnétique, par effet Zeeman le spin du centre coloré est couplé à la position de l’oscillateur. On a pu ainsi montrer que les vibrations de l’oscillateur sont encodées sur le spin électronique. Ce projet vise à explorer de nouveaux mécanismes de couplage dans ces systèmes hybrides et à étudier le couplage spin-oscillateur en sens inverse, c'est-à-dire d’encoder l’état du spin électronique sur la position de l’oscillateur, reproduisant ainsi l’expérience de Stern et Gerlach avec des objets macroscopiques.

Pour ce faire, une sensibilité en force extrême est requise car la force exercée par le spin sur l’oscillateur est de l’ordre de ~20 aN pour un gradient de 1e6 T/m. De tels niveaux de sensibilité sont accessibles avec des oscillateurs mécaniques de très faible masse, comme démontré à température ambiante sur les nanofils de SiC [2]. De même, il est nécessaire de lire avec une grande précision les vibrations de ces nanofils. Les travaux en cours au laboratoire démontrent que la lecture optique des vibrations de nanofils permet de résoudre avec une grande dynamique leur mouvement Brownien. Enfin des protocoles avancés de manipulation du spin électronique ont également été mis en œuvre [3] au laboratoire qui ont permis de mettre en évidence la synchronisation du spin sur la vibration mécanique [5]. On a ainsi pu observer l’analogue phononique du triplet de Mollow en électrodynamique quantique, apparaissant lorsque le qubit de spin est fortement excité par les vibrations du nanofil. [1] O. Arcizet et al, Nature Physics 7, 879 (2011). [2] A. Gloppe et al, Nature Nanotechnology (2014). [3]S. Rohr et al., PRL 112, 010502 (2014) [4] B. Pigeau et al, Nature Communications ( 2015). [5] L. Mercier de Lépinay et al., arXiv:1503.03200 (2015). Interactions et collaborations : NEEL, ENS Cachan, labo. Kastler Brossel, Uni-Basel. Ce stage pourra se poursuivre par une thèse Formation / Compétences : Ce travail de thèse permettra d’acquérir un savoir-faire en nano-optique, en nanosciences et en manipulation de système quantiques. Même si ce projet revêt un fort caractère expérimental, l’aspect novateur des systèmes hybrides nanomécaniques requiert un intérêt poussé pour la formalisation théorique. Contact : Arcizet Olivier- Benjamin Pigeau, Institut Néel - CNRS : 04 76 88 12 43 [email protected] [email protected] Plus d’info. sur : http://neel.cnrs.fr



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Electric field manipulation of skyrmions

General Scope: Downscaling magnetic film thickness to the nanometer range allows to evidence new lengthscales. New physical effects are enhanced and dominate the usual effects. Nanomagnetism is the research field where these new behaviours are studied. Due to the constant need for larger and larger information storage and information processing densities, such fundamental studies are associated to the development of new magnetic devices (sensors, memories, oscillators …). Downsizing the lateral size of structures, allows for the study of isolated magnetic entities such as single magnetic domains, or individual magnetic domains walls. The ultimate magnetic domain could take the shape of a skyrmion structure, which is a topologically stabilised nano-object, where a non collinear interaction (the Dzyaloshinskii-Moriya interaction) plays a crucial role. The existence of such an isolated object in an ultra-thin metallic ferromagnetic film has been speculated for the last few years. Finally, the creation and manipulation of such a skyrmion bubble using an applied magnetic field or a spin-polarised current has recently been published (W. Jiang et al. Science July 2015). Research topic and facilities available: In 2016 we have demonstrated in our researche group the reproducible and controled nucleation and annihilation of skyrmions using electric field gating, an energy efficient and easily integrable solution. These results constitute an important step toward the use of skyrmions in functional magnetic devices. The aim this work is to further use electric gating to control the position of the nucleated skyrmions. For that the skyrmion will be displaced using an electric current and the electric field will be used to stop or allow the skyrmion propagation.

Possible collaboration and networking: The environment will be the micro and nanomagnetism (MNM) research group of Institut Néel. with interactions with the Deposition, Magnetometry and Nanofab technical groups. The student will work together with a third year PhD student working on a close subject. The student can possibly continue the subject in the framework of a PhD starting in 2017. Possible extension as a PhD:yes Required skills: Solid state physics with a taste for experimental studies. Interest for fabricating magnetic model systems, detailed studies and quantitative modeling. Starting date: spring 2017 Contact: Name: Anne Bernand-Mantel, Laurent Ranno Institut Néel – CNRS e-mails: [email protected], [email protected]

More information: http://neel.cnrs.fr



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Non-equilibrium quantum modeling of nano-structure based solar cells

Cadre général : Nowadays, because of growing energy demand, exhaustion of oil resources, and global warming issues, the world is in need of alternative energy sources. Solar energy is one of the clean, renewable and available energy sources and great attention is given to new solar cells concepts based in particular on nanostructures or molecular systems. Sujet exact, moyens disponibles : The development of new type of solar cells requires an accurate, reliable and comprehensive simulation of the designed structures. Theoretical modeling of such systems has been a challenging task for several years and we have developed a new simple non-equilibrium quantum formalism. This approach can be applied to two level models of photo-cells (see figure) and current efforts includes its application to more realistic models of molecular photocells or quantum dots. During its internship the student will learn basic aspects of the formalism which relies on the quantum scattering theory. He /she will participate to comprehensive simulation for simple models of nanosized solar cells. The student must be able to use Fortran codes. Computational ressources are available at Institut Néel.

Figure 1: Two level model. The photon is absorbed in the central part (molecule/ quantum dot) and creates an electron in the upper level and a hole in the lower level. The electron (hole) can be evacuated through the right (left) lead. The net result of the absorption of a photon is the transfer of an electron from the left to the right lead. Interactions et collaborations éventuelles : Currently, we have strong collaborations with scientific groups from Canada, USA and Iran. Ce stage pourra se poursuivre par une thèse (ou ce sujet est limité à un stage M2...). The formalism developed in the team is new and opens an active area for several years. The student can continue this subject as a PhD thesis. Formation / Compétences : Quantum mechanics - Programming and analysis skills and having teamwork abilities. Période envisagée pour le début du stage : March or April 2017 Contact : Mayou Didier Institut Néel - CNRS : Tel : 04 76 88 74 66 mel : [email protected] Plus d'informations sur : http://neel.cnrs.fr

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