WorldCat Identities

Gabay, Marc F. (19..-....).

Overview
Works: 17 works in 23 publications in 2 languages and 24 library holdings
Genres: Academic theses 
Roles: Thesis advisor, Opponent, Other, Author
Publication Timeline
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Most widely held works by Marc F Gabay
THEORIE PHENOMENOLOGIQUE DES SUPRACONDUCTEURS DE TYPE II by HUI ZHENG( Book )

2 editions published in 1998 in French and held by 3 WorldCat member libraries worldwide

LES SYSTEMES DE SPINS XY FRUSTRES (FXY) SONT UTILISES POUR L'ETUDE DES FLUCTUATIONS THERMIQUES DES SUPRACONDUCTEURS A HAUTE T#C. LE PARAMETRE DE FRUSTRATION F = 1/3 CORRESPOND AU CAS D'UN CHAMP FORT. NOUS ETUDIONS CE PROBLEME SUIVANT DEUX VOIES : ANALYTIQUE ET SIMULATION NUMERIQUE. DANS LA PARTIE ANALYTIQUE, LA METHODE SCHA N'ARRIVE PAS A DECRIRE LES FLUCTUATIONS DE CHIRALITE DANS LES SYSTEMES FXY. NOUS UTILISONS UNE MODIFICATION DE SCHA - NSCHA, QUI CONTIENT UN TERME SUPPLEMENTAIRE DECRIVANT LE COUPLAGE ENTRE LES CHIRALITES. LE CALCUL EN NSCHA COINCIDE TRES BIEN AVEC LE RESULTAT DE LA SIMULATION MONTE CARLO DANS LA REGION BASSE TEMPERATURE JUSQU'A T#C. NOUS APPLIQUONS ENSUITE NSCHA AUX PLANS FXY F = 1/3 FAIBLEMENT COUPLES AVEC LE PARAMETRE DE COUPLAGE = 0.1. NOUS TROUVONS QUE #X#X ET #Z#Z S'ANNULENT A PEU PRES EN UN MEME POINT : ON NE VOIT PAS DE SIGNE DE DECOUPLAGE DES PLANS. DANS LA PARTIE RELATIVE AUX SIMULATIONS MONTE CARLO, NOUS PRESENTONS DES ANALYSES EXTENSIVES SUR LES SYSTEMES 2D ET 3D ANISOTROPES. A BASSE TEMPERATURE, LES SYSTEMES MONTRENT UNE STRUCTURE EN ESCALIER, LES VORTEX-CHARGES S'ORGANISENT EN RANGEES QUI SE PROLONGENT SELON UNE DIRECTION DIAGONALE DU RESEAU CARRE. A 2D, NOUS TROUVONS QUE LE SYSTEME A PLUTOT UNE SEULE TRANSITION DONT L'UNIVERSALITE EST DE TYPE ISING. A 3D, AUX BARRES D'ERREURS PRES, NOUS TROUVONS QUE T#Z T#. CELA DIFFERE DES RESULTATS POUR F PETIT QUI CORRESPOND AU CHAMP FAIBLE, QUI TROUVENT PLUTOT DEUX TRANSITIONS DONT L'UNE SERAIT DU PREMIER ORDRE. NOTRE LIMITE F = 1/3 CORRESPOND AU CAS D'UN CHAMP MAGNETIQUE FORT. DE PLUS, LA STRUCTURE EN ESCALIER DE VORTEX CORRESPOND A UN EFFET DE CHAMP INCLINE AU LIEU D'ETRE PERPENDICULAIRE AUX PLANS CUO. LA FUSION DU RESEAU DE VORTEX ET LA PERTE DE COHERENCE DE PHASE DANS LES PLANS CUO ET DANS LA DIRECTION Z SE PRODUISENT A UNE MEME TEMPERATURE. LA TRANSITION SEMBLE ETRE CONTINUE, CE QUI EST PROBABLEMENT UN EFFET DE CHAMP FORT. DANS LA DERNIERE PARTIE, NOUS CONSIDERONS L'EFFET DE DESORDRES SUR UN PLAN FXY F = 1/3. NOUS NOUS SOMMES LIMITES A UN DEFAUT DE LIENS
Effets d'une impureté non magnétique dans la phase normale des cuprates supraconducteurs by Eric Semel( Book )

2 editions published in 2005 in French and held by 2 WorldCat member libraries worldwide

THE ADJONCTION OF IMPURITIES TO TEST THE PROPERTIES OF MARERIALS IS A WELLKNOWN TECHNIC, AND IS USED SINCE THE DISCOVERY OF SUPERCONDUCTIVITY IN CUPRATES. NMR EXPERIMENTS SHOW THAT A NON MAGNETIC IMPURITY LEAD TO A MAGNETIZATION AROUND THE IMPURITY. ITS OSCILLATIONS IS A MANFESTATION OF STRONG ANTIFERROMAGNETIC CORELATIONS. THE MODEL I HAVE USED IS THE t-t'-J HAMILTONIEN ON SCARE LATTICE, WHICH REPRESENTS THE CuO2 PLAN. THIS HAMILTONIEN, TRANSFORMED BY THE USE OF THE SLAVE-BOSONS FORMALISM, IS TREATED BY A MEAN FIELD APPROXIMATION. THE DEVELOPPED MODEL CONSIDERS AN UNIQUE IMPURITY REPRESENTED BY AN EXCLUDE SITE, IN ACCORDANCE WITH EXPERIMENTS SHOWING THAT THE EFFETCS OF THE PRESENCE OF IMPURITIES ARE PROPORTIONNEL TO THE IMPURITIES CONCENTRATION (NO INTERACTION BEETWEN THE IMPURITIES). IN THIS FORM, THE PROBLEM IS EXPRESSED AS A TWO FREE GAZES PROBLEM, A " SPINONS " GAZ (SPINS DEGREES OF FREDOM) AND AN " HOLONS " GAZ (CHARGES DEGREES OF FREDOM), WITCH INTERACTED ONE WITH THE OTHER. THE PARTICULES DIFFUSE ON THE IMPURITY. THE MAGNETIZATION IS FOUND BY SOLVING A SELF-CONSISTENT EQUATIONS SYSTEM. THE MEAN MATHEMATIC TOOL IS THE GREEN FUNCTION, WHICH IS THE PROPAGATOR OF SPINONS AND HOLONS BEETWEN TWO SITES ON THE SCARE LATTICE. THE RESULTS I HAVE OBTAINED ARE IN GOOD AGREEMENT WITH EXPERIMENTS. I FIND A STAGGERED MAGNETIZATION AROUND THE IMPURITY, WITH AN ENVELOP THAT DECREASES AS A BESSEL FUNCTION. THE TYPICAL length ASSOCIATED WITH THIS BESSEL FUNCTION, ASSIMILATED TO THE MAGNETIC CORRELATION length, IS OF ORDER OF FEW LATTICE PARAMETER, AND ITS VARIATION WITH DOPING AND TEMPERATURE ARE SIMILAR TO EXPERIMENTS. THE SAME ACCORDANCES ARE FOUND FOR THE OTHERS PHYSICAL QUANTITIES (CURIE-WEISS TEMPERATURE, SUSCEPTIBILITY,...)
Effets d'orbitale sur des systèmes de fermions fortement corrélés à basse dimension by Torsten Becker( Book )

2 editions published in 2001 in French and held by 2 WorldCat member libraries worldwide

In this thesis we consider with orbital effects on highly correlated low dimensional fermion systems by considering in more detail the two models of a CuO chain and a Cu2O5 ladder, which are representative of all one-dimensional models that include several atoms or molecules per unit cell. For the half-filled or doped CuO chain model, we obtain different behaviors of the correlation functions depending on the site. These different behaviors of copper and oxygen sites change as a function of temperature, charge gap and doping. From this study we deduce a scenario for the Knight shift and relaxation time associated with NMR measurements. This scenario resembles that observed in high T(c) cuprates: the temperature behavior of the copper and oxygen Knight shifts is identical, where as the temperature behavior of the copper and oxygen relaxation times differs. This orbital effect is produced within the framework of the Luttinger and LutherEmery liquid theory and is impossible to deduce within the framework of the Fermi liquid theory. For the CU2O5 ladder model, the inclusion of the internal structure results in an effective bosonic model which can not be integrated into the exhaustive class of ladders studied up to now, because of an existent asymmetry of the bosonic densities in the 0 and the pi channel. In the limit of small local repulsions a phase diagram in function of the asymmetry is established. It shows the existence of other phases beside the usual d-wave superconducting phase
Ground state phase diagram and effects induced by non-magnetic impurities in doped two-leg Cu-O hubbard ladders by Piotr Chudzinski( Book )

2 editions published in 2008 in English and held by 2 WorldCat member libraries worldwide

Thèse rédigée entièrement en anglais
Etude du modèle de Hubbard bidimensionnel dans l'approche du modèle sigma non linéaire effectif by Karol Borejsza( Book )

2 editions published in 2004 in French and held by 2 WorldCat member libraries worldwide

WE STUDY MAGNETIC AND ONE-PARTICLE PROPERTIES OF THE 2D HUBBARD MODEL WITHIN THE FRAMEWORK OF A NON-LINEAR SIGMA MODEL (NLSM) DESCRIPTION OF SPIN FLUCTUATIONS THE THEORY RESTS UPON THE ASSUMPTION OF LOCAL ANTIFERROMAGNETIC (AF) ORDERING. IT IS VALID AT ALL COULOM INTERACTION STRENGTHS, BELOW A CROSS-OVER TEMPERATURE MARKING THE ONSET OF AF SHORT-RANGE ORDER. AT HALF-FILLING, WE DERIVE THE MAGNETIC PHASE DIAGRAM AND COMPUTE THE FERMION SPECTRAL FUNCTION. AT ZERO TEMPERATURE, LONG-RANGE AF ORDER IS SHOWN TO BE PRESENT FOR ALL VALUES OF THE COULOMB REPULSION. THE GROUND-STATE EXHIBITS A SMOOTH TRANSITION FROM A SLATER-LIKE BEHAVIOR AT WEAK COUPLING, TO A MOTT-HEISENBERG-LIKE BEHAVIOR AT STRONG COUPLING. AT FINITE TEMPERATURES THE AF ORDER IS SUPPRESSED, IN AGREEMENT WITH THE MERMIN-WAGNER THEOREM, BUT THE AF CORRELATION LENGTH REMAINS EXPONENTIALLY LARGE WITH RESPECT TO THE LATTICE SPACING, WE DEVELOP A NEW TECHNIQUE FOR CALCULATING THE SPECTRAL FUNCTION AND THE DENSITY OF STATES, WHICH TAKES INTO ACCOUNT THE HIGHLY NON-GAUSSIAN NATURE OF MAGNETIC FLUCTUATIONS. WE ESTABLISH THE EXISTENCE OF A TRANSITION BETWEEN A WEAK-COUPLING REGIME EXHIBITING A PSEUDOGAP AT FINITE TEMPERATURES, AND A STRONG-COUPLING REGIME WHERE ONE-PARTICLE EXCITATIONS ARE GAPPED. THE PROPERTIES OF BOGOLIUBOV QUASI PARTICLES AT ZERO TEMPERATURE AND OF THEIR PRECURSORS AT FINITE TEMPERATURES ARE ANALYZED. AWAY FROM HALF FILLING, A NEW METHOD FOR DERIVING THE LOW-ENERGY EFFECTIVE ACTION IS PROPOSED. THE EFFECTIVE MODEL INVOLVES LOW-ENERGY BOGOLIUBOV QUASI PARTICLES COUPLED TO A NLSM. THE LOW-ENERGY ACTION IS CRITICALLY COMPARED TO KNOWN PHENOMENOLOGICAL NLSM-FERMION THEORIES
Ordres non conventionnels et entrelacés du modèle de Hubbard à basse dimensionnalité by Alexandre Leprévost( Book )

2 editions published in 2015 in French and held by 2 WorldCat member libraries worldwide

La compréhension de la supraconductivité à haute température critique exhibée par certains oxydes de métaux de transition demeure une question centrale en physique théorique de la matière condensée. Depuis la proposition historique de P.W. Anderson, le modèle de Hubbard répulsif en géométrie bidimensionnelle est devenu un paradigme pour tenter de capturer les propriétés essentielles des matériaux supraconducteurs non conventionnels. Cependant, la détermination de son état fondamental exact se heurte à la complexité exponentielle du problème quantique à N-corps. Dans cette thèse, nous poursuivons l'objectif de développer un schéma variationnel d'approximation s'affranchissant de toute hypothèse concernant les ordres magnétiques, de charge ou supraconducteurs susceptibles d'émerger de l'Hamiltonien à basse énergie. L'approche trouve son originalité dans l'introduction de corrélations par la restauration, avant variation, de symétries délibérément brisées dans un état d'essai en forme d'une superposition de fonctions d'onde versatiles de type Hartree-Fock et Bogoliubov-de Gennes. Pour des amas à deux et quatre sites, nous montrons analytiquement que cette méthode de champ moyen enchevêtré par les symétries de l'Hamiltonien permet de retrouver l'état fondamental exact quelle que soit l'intensité des interactions. Pour de plus grands réseaux dopés en trous et dans les régimes fortement corrélés, nous mettons en exergue un arrangement des moments magnétiques en spirale ou suivant une onde de densité de spin qui est alors accompagnée d'inhomogénéités sous forme de rayures périodiquement réparties. Ces ordres sont de plus entrelacés avec des corrélations d'appariement en onde d à longue distance qui, à la limite thermodynamique, signent la supraconductivité. Ces résultats sont obtenus via des simulations systématiques dans une géométrie de tubes de plaquettes réalisable expérimentalement à l'aide d'atomes froids piégés dans des réseaux optiques
Ultrafast electron dynamics in Mott materials by Gabriel Lantz( )

1 edition published in 2015 in English and held by 1 WorldCat member library worldwide

Les isolants de Mott sont un exemple parfait de l'impact des corrélations électroniques locales sur les propriétés macroscopiques des matériaux. En variant légèrement le dopage ou la pression, un métal peut se transformer en un isolant. Ces propriétés peuvent être modifiées de manière très rapide en plaçant ces matériaux loin de l'équilibre. Nous avons étudié un prototype de Mott-Hubbard, V2O3 dopé en Cr, en utilisant l'état de l'art des techniques pompe-sonde, à savoir la photoémission résolue en angle, la réflectivité optique, la spectroscopie THz, et la diffraction des rayons X. La réponse électronique du système, après une excitation laser femtoseconde, qui a été maintenue pour chaque expérience à une longueur d'onde de 800 nm, a pu être déconvoluée de la réponse du réseau. Une étude comparative de ces réponses transitoires démontre un fort couplage électron-phonon dans ce prototype de matériau fortement corrélé. Avant thermalisation, le poids spectral est transféré de la bande de Hubbard inférieure vers le gap de Mott. Sur une échelle de temps plus long un état métastable est stabilisé par un changement structural. Pour mieux comprendre la réponse transitoire des isolants de Mott, nous avons également étudié un autre composé de Mott, BaCo1-xNixS2. Les tendances générales des isolants de Mott après photoexcitation ont été analysées en utilisant un modèle à deux orbitales. Nous interprétons que le remplissage du gap comme un changement spécifique des occupations orbitales
Hétérostructures supraconductrices et isolants topologiques by Oliver Hijano Cubelos( )

1 edition published in 2015 in French and held by 1 WorldCat member library worldwide

The thesis is focused on the theoretical study of the electronic properties at the surface of the transition metal oxide STO. This material is the cornerstone of oxide electronics, an emerging research area that has the goal of investigating transition metal oxides as post-silicon candidates for a future emerging new electronics. STO is in itself an astounding system; in its purest chemical composition is a good ban-insulator with a wide bandgap. Nevertheless, upon doing it with tiny amounts of other elements it transforms itself in a metal with high electron mobility. Even more remarkably, at the lowest temperatures, typically below 300mK, it goes superconductor. And adding to these properties, strain induces also ferroelectricity in this material. Over the last years, STO has also grabbed attention because of its ability of hosting two-dimensional electron gas (2DEGs) when it is interfaced with some polar oxides. Such 2DEGs exhibit fascinating properties, the most conspicuous is the coexistence of magnetism and superconductivity.The surface of STO can host 2DEGs too, without need of interfacing it to other materials; in this case the electrons participating in transport are generated by oxygen vacancies created at the surface. This is remarkable observation, as it affords a simpler structure where the 2DEGs properties can be studied. In spite of the accumulated knowledge, still a better fundamental comprehension is required of the electronic structure of the quantum wells at the surfaces oriented along the 111 direction, for which the perovskite structure is reminiscent of the celebrated honeycomb-like structure of graphene. Contrary to the latter, in which electrons are in s- and p- states, 111 quantum wells in STO would host electrons in d-bands. Higher electronic correlations are then expected, that may bring new fascinating physics.The outline of this Thesis has two main branches: first, it studies the 111-oriented STO bilayer, formed by just two unit cells; secondly it analyzes the quantum wells generated by Oxygen vacancies at the 111-surface of STO. Both subjects are approached using tight-binding models in which the Hamiltonian incorporates different terms related to on-site energies, hopping interactions or spin-orbit coupling. From these calculations, I have carried out an exhaustive analysis of the orbital character and parity properties of valence and conduction bands, as well as edge states in the 111 bilayer. Tight-binding calculations have also shed light on the orbital character, space location and extension and energy of electronic states generated by oxygen vacancies at the 001 surface of STO
Orbital-selectivity in strongly correlated fermionic systems. From materials to cold-atoms by Emilio Winograd( )

1 edition published in 2013 in English and held by 1 WorldCat member library worldwide

This thesis focuses on multiorbital aspects of strongly correlated fermionic systems. In particular, it focuses on the existence of orbital differentiation in which coexistence of itinerant and localized character can be associated to different orbitals. This subject is discussed in the context of cold atoms and materials, providing a bridge between both communities.In the first part of the thesis, we give an insight into the problem of strong correlations in materials, and we introduce the concept of 'orbital-selective Mott transition'. We also provide the main tools to understand how materials can be simulated with cold atoms experiments, and we present important related results in the context of the metal-Mott insulator transition. The technical aspects, based on dynamical mean-field theory are also discussed, and the solution of two key models of strongly correlated fermionic systems, i.e., the Hubbard model (HM) and the Falicov-Kimball model (FKM), are reviewed.Then we study in detail the physics of two interacting fermionic species with different masses in an optical lattice. We establish the different phases (with and without long-range order) in terms of the interactions strength (U), mass ratio and temperature (T), and also discuss the thermodynamic variables, which are relevant in cold atoms experiments. We show that in the metallic phase (U below a critical value) and for some degree of mass imbalance, a crossover appears between a Fermi-liquid metallic state at low T, and an 'orbital-selective' state at higher T, where the heavy fermions effectively localize while the light species remain itinerant. Hence, we propose this minimal model for addressing orbital-selective physics with cold atoms experiments.Based on the properties of the studied model, we propose the 'entropic chromatography' as a new method for cooling fermionic atoms in optical lattices. We discuss its efficiency and limitations, and provide some ideas in order to overcome them.In the last part of the thesis we generalize the previous model to a model relevant for multiband correlated materials that can display orbital differentiation. We show that the orbital-selective Mott state can be stable under lattice distortions modeled by local hybridization between the orbitals. However, the Mott state is characterized by a pseudogap, where charge fluctuations abruptly reduce, but the state remains compressible. In connection with the previous model, we discuss the temperature-induced orbital-selective crossover in this problem, we compare our results with photoemission experiments, and predict what would happen in materials that display local hybridization between the bands
Etude de la thermodynamique des verres de spin dans le cadre du champ moyen et de phénomènes critiques dans les cristaux liquides et les polymères by Marc F Gabay( Book )

1 edition published in 1981 in French and held by 1 WorldCat member library worldwide

The author will first present the problem from the thermodynamics point of view. The difficulties encountered in a mean field theory will be analyzed, the mathematical methods employed will be described, and the results of the calculations will be presented. This enables one to display the behavior of spin glasses and to proceed from the microscopic theory to an experimental phenomenology
De l'impureté Kondo aux états liés dans les supraconducteurs by Sébastien Guissart( )

1 edition published in 2016 in French and held by 1 WorldCat member library worldwide

In this thesis, I was mainly interested in the effects related to magnetic impurities in metals and superconductors.In the first chapter I will present the Kondo effect, this effect occurs when a magnetic impurity exhibits an antiferromagnetic coupling with the metal that it pollutes. The electrons then form, at a sufficiently low temperature, a cloud screening the magnetism of the impurity. The second chapter will focus on the states of Yu-Shiba-Rusinov products by magnetic impurities in a superconductor. In this case, the impurity locally breaks the superconducting order and a quantum state is created inside the gap.Some so-called topological materials may include quantum states protected at their edges against external perturbations. In the last two chapters, I will present the properties of topological superconductors and their edge states. In the third chapter I will present the different topological phases that can include a superconductor with a parameter of complex order mixing waves p and s in the presence of a Zeeman field.In the fourth and last chapter I will present a study of the states of edge that may include this type of superconductors
Effets d'une brisure de symétrie sur les stuctures électroniques d'URu2Si2 et de KTaO3 by Cédric Bareille( )

1 edition published in 2013 in French and held by 1 WorldCat member library worldwide

Several physical properties of a system can be understood by looking at the symmetries involved. Breaking of a symmetry affects the behavior of the system, regardless ifit happens spontaneously or not. This is observed with the emergence of the mass inparticle physics models, or with the diverse phases arising in condensed matter systems,as magnetism or superconductivity. Using angle-resolved photoemission spectroscopy (ARPES), this work studies theeffects of a symmetry breaking for two different systems : the heavy fermion systemURu2Si2 and the transition metal oxide (TMO) KTaO3. In URu2Si2, a transition occurs from a paramagnetic phase at T>THO to the hiddenorder phase at T<THO, with THO ≈ 17.5 K. This new order potentially breaks several symmetries. Although this transition was measured almost thirty years back, usingelectrical transport, no theoretical model could yet bring a consensus in the community. Since then, various characterizations of this system have been realized, howevermomentum-resolved informations are still missing to help unravel this mystery. Thus,during this thesis, we used state-of-the-art ARPES setups to measure several gaps located at different points in the Brillouin zone, and with amplitudes below 10 meV. Someof them are related to the Kondo coherence, and one is the hidden order gap. We showthat these measurements are consistent with previous experimental works. Finally, weobserved that our measurements differ from LSDA calculations solely by a renormalization of the effective masses by, at least, a factor 10 close to the Fermi level. Taking intoaccount some interactions, such as electronic ones, could lead to a more accurate model.Our measurements provide the constraints for this possible modeling. Unlike the transition we just described, the symmetry breaking in potassium tantalate KTaO3 is not spontaneous. In this system, we look at the (111) surface, wherethe translation symmetry is broken. A metallic two-dimensional electron gas (2DEG)has been measured in 2004 by Ohtomo at the interface between two insulating TMOs :strontium titanate SrTiO3 and lanthanum aluminate LaAlO3. The possible electronicapplications of exotic properties in TMOs, resulting from the d orbitals, has brought anew wave of activity to this topic. Later, our group measured 2DEGs at the (001) baresurfaces of SrTiO3 and KTaO3. Following these results, we wished to tailor the characteristic of such 2DEGS. Led by the theoretical prediction of states with non-trivialtopological character, we are presenting the evidence of a 2DEG at the (111) surface ofKTaO3. We also discuss its dispersion and introduce a tight binding calculation modelsuccessfully. This work is a step towards the realization of non-trivial topological statesin transition metal oxides
Spin-to-charge current conversion in SrTiO3-based two-dimensional electron gases by Diogo Castro Vaz( )

1 edition published in 2018 in English and held by 1 WorldCat member library worldwide

Ce travail présente l'étude de la conversion courant de spin en courant de charge dans les gaz d'électrons bidimensionnels à base de SrTiO3. Nous commençons par une présentation des concepts de base de la spintronique : le spin, une définition du courant de spin et le comportement des spins dans des matériaux, les principales conséquences de la relation entre les courants de charge et de spin dans différents matériaux, et comment un courant de charge peut être converti en un courant de spin (et vice versa). Dans des scénarios spécifiques, la physique de l'interconversion suit des considérations de symétrie particulières dans le cadre des effets de Dressllehaus et de Rashba, qui expliquent l'interconversion du courant de charge/spin dans les gaz d'électrons 2D via l'effet direct et inverse d'Edelstein. Dans le deuxième chapitre, nous présentons le principal matériau utilisé dans cette thèse: le titanate de strontium (SrTiO3). Après avoir analysé ses principales caractéristiques, nous explorons le gaz d'électrons 2D présent dans le système LaAlO3/SrTiO3. Nous discutons en détail de l'origine de la conductivité interfaciale entre ces deux isolateurs, l'épaisseur critique de conduction de 4 mailles de LaAlO3 et des principaux mécanismes conduisant à la formation du gaz électronique 2D (catastrophe polaire, interdiffusion de cation, réactions à la surface et défauts induits par la polarité). Ensuite, nous décrivons en détail la procédure expérimentale pour obtenir des hétérostructures de LaAlO3/SrTiO3: le traitement de surface des monocristaux de SrTiO3, la croissance par ablation laser pulsé de films ultra-minces de LaAlO3, et la pulvérisation cathodique. Nous introduisons les deux techniques principales utilisées pour évaluer les propriétés interfaciales, la spectroscopie photoélectronique de rayons X (XPS) et le magnétotransport, avec quelques résultats pour les échantillons de LaAlO3/SrTiO3. Enfin, nous montrons comment un mince dépôt d'une couche métallique sur LaAlO3/SrTiO3 peut modifier radicalement les propriétés interfaciales en réduisant (si le métal est réactif et possède un travail de sortie inférieur à une valeur critique) ou en augmentant (pour les métaux nobles) l'épaisseur critique de la conduction interfacial. Pour conclure ce chapitre, nous proposons un modèle qui décrit comment un gaz d'électrons 2D peut être créé dans d'autres systèmes à base d'oxydes complexes. Dans le troisième chapitre, nous étudions les phénomènes de conversion spin/charge. Nous commençons par un état de l'art de la littérature concernant des observations expérimentales des gaz d'électrons Rashba 2D, ainsi que de la conversion du courant spin-à-charge par l'effet Edelstein inverse dans les puit de potentiel à base de semi-conducteurs, les isolants topologiques et les systèmes à base d'oxydes. Ensuite, nous introduisons le pompage de spin, une technique utilisée pour générer des courants de spin purs. Les résultats de la conversion du courant spinà-charge dans les systèmes LaAlO3/SrTiO3 et metal/SrTiO3 sont présentés, accompagnés d'une interprétation de la géante et ajustable con-version spin/charge. Dans le cas d'échantillons composés par metal/SrTiO3 , la spectroscopie photoélectronique résolue en angle (ARPES) et les notions de mélange de bande électronique et de topologie sont introduites pour justifier la conversion charge/spin extrêmement élevé. Dans le dernier chapitre, nous montrons des expériences supplémentaires réalisées sur le système LaAlO3/SrTiO3 en ce qui concerne la magnétorésistance anisotrope et unidirectionnelle [...]
Etats topologiques aux surfaces de perovskites d'oxydes de métaux de transition by Manali Vivek( )

1 edition published in 2018 in English and held by 1 WorldCat member library worldwide

The subject of topology in oxides, in particular at the surfaces of perovskite oxides like SrTiO₃, or at the interface of LaA1O₃/SrTiO₃ will be investigated in this thesis. Both compounds, at their (001) oriented surfaces, contain a metallic state confined to a few nanometers at the surface. In addition, we will show that there exist certain three band crossings around which perturbations will cause an inverted and gapped band spectrum to appear. These will lead to topological edge states which can be detected via induced superconductivity as in the case of topological quantum wells or superconductor-semiconductor nanowires. Next, the (111) oriented surface of LaA1O₃/SrTiO₃ will be studied where Hall transport measurements reveal a one to two carrier transition via electrostatic doping. An explanation based on a tight binding modelling including Hubbard U correlations, will be proposed which will give rise to band crossings between sub-bands promoting topological states. Finally, an ab-initio study of CaTiO₃ will be performed to explain the metallic state which exists at its (001) oriented surface and to predict magnetism in the system. CaTiO₃ is different from the other compounds studied previously, due to the large rotation and tilting of the oxygen octahedra surrounding the Ti, which complicates the picture. The structure with and without oxygen vacancies will be studied in-depth to provide details about the conduction band and their orbital characters
Théorie de Boltzmann chirale pour le transport dans les multicouches, électrons et photons, balistique et diffusif by Nicolas Charpentier( )

1 edition published in 2012 in French and held by 1 WorldCat member library worldwide

Cette thèse aborde le problème du transport diffusif dans les matériaux multicouches lorsque l'épaisseur des couches est comparable voire plus petit que le libre parcours moyen. Nous présentons un formalisme qui à la fois effectue une synthèse et permet d'aller au delà des divers modèles existants, dérive-diffusion, le modèle Valet-Fert, la méthode des flux ou encore le modèle de Fuchs-Sondheimer. Ce formalisme est applicable à deux types de structures: (i) la géométrie dite CPP (Current Perpendicular to Plane) où le courant moyen est perpendiculaire aux interfaces séparant les couches, et (ii) la géométrie dite CIP (Current In Plane) où le courant moyen est parallèle aux interfaces. Ce nouveau modèle de transport est bâti à partir d'une équation de Boltzmann où les collisions dans les couches et aux interfaces sont représentées par des intégrales de collision linéaires pouvant décrire aussi bien des réflexions spéculaires que des collisions aléatoires non nécessairement isotropes. La résolution de cette équation de Boltzmann pour déterminer les quantités macroscopiques locales d'intérêt se fait en trois étapes : pour chacune des couches, (1) la distribution locale des particules est séparée en deux « chiralités » caractérisés par le signe de la projection du vecteur vitesse de chaque particule le long de l'axe perpendiculaire aux interfaces ; (2) la description locale complète de la distribution angulaire des vitesses pour chaque chiralité est obtenue en développant sur une nouvelle base polynômes orthogonaux adaptée à l'existence de deux chiralités ; (3) pour effectuer la moyenne chirale sur la distribution angulaire des vitesses on définit une troncature minimale de ce développement adaptée aux quantités macroscopiques locales d'intérêt.L'étape (1) est nécessaire afin de pouvoir décrire correctement les collisions d'interfaces, l'étape (3) est usuelle mais l'ingrédient clef de ce formalisme est le point (2) qui seul permet de rendre cohérent les étapes (1) et (3) en présence d'interfaces. Pour la géométrie CPP, ce formalisme « Boltzmann chiral » permet d'unir les systèmes balistique et diffusif sous une même approche macroscopique. En présence de polarisation en spin, ce nouveau formalisme permet d'obtenir entre autre les résistances d'interfaces du modèle Valet-Fert en fonction des coefficients de transmission généralisés associés aux collisions d'interface. Pour les structures CIP, ce modèle permet d'obtenir des expressions analytiques pour les conductivités locales par couche (avec ou sans polarisation en spin) et de plus il rend le lien avec le transport CPP plus transparent. Ce formalisme n'étant pas propre au transport électrique, nous montrons sa versatilité sur une application au transport lumineux en revisitant le problème de Milne pour lequel nous retrouvons un résultat exact de façon beaucoup plus simple. Nous présentons pour terminer une méthode variationnelle fournissant une interprétation intéressante du modèle de Fuchs-Sondheimer
Nouveaux états électroniques d'interface à partir d'isolants corrélés by Mathieu Grisolia( )

1 edition published in 2016 in English and held by 1 WorldCat member library worldwide

Transition metal oxides (Ti, Fe, Mn, Cu, etc.) display a multitude of features while crystallizing in a reduced number of structures. This is the case for example of perovskites which exhibit many electronic (insulators, metals, superconductors) and magnetic (ferro- and antiferromagnetic) orders. Their structural compatibility offers a unique playground for combining them in the search for new interfacial properties. A typical example discovered in 2004 is LaAlO₃ and SrTiO₃ whose interface reveals a high-mobility electron gas although the parent constituents are two conventional band insulators.Following-up on this major achievement, this thesis aims at generating new electronic interfacial phases, not from band insulators but rather from Mott and charge transfer insulators. At the interface between these types of compounds, band alignment is made more complex by the presence of strong correlations between electrons.Hence, interfacial reconstructions can destabilize the ground state, and generate new phases absent from the phase diagrams of the two building blocks.Initially, we synthetized, by pulsed laser deposition, a typical Mott insulator, rare earth titanates (RTiO₃ ) in the form of thin layers, which were optimized and characterized on different substrates.Secondly, we also grew charge transfer insulators, rare earth nickelates (RNiO₃ ). We specifically studied the effect of the ionic radius of the rare earth on the electronic structure of these compounds at low temperature.The core of this thesis is to study the interface formed by these two constituents via a combination of spectroscopic techniques (synchrotron radiation-based absorption, XAS, linear and circular dichroism XMCD and energy loss spectroscopy, STEM-EELS) in connection with ab-initio calculations.After demonstrating the emergence of a new ferromagnetic phase in nickelates, absent of the bulk phase diagram, we discuss in particular the role of correlations in nickelates on the charge transfer and magnetic reconstruction, observed at the interface with GdTiO₃ .Finally, we will propose a new external knob, light, to alter the level of covalence in nickelates without changing the rare earth. These results open the way for new devices taking advantage of the active control of the level of covalence in charge transfer insulators
Phases désordonnées dans des gaz d'atomes froids de basse dimensionnalité by François Crépin( )

1 edition published in 2011 in French and held by 1 WorldCat member library worldwide

In this thesis we study two distinct problems related to the physics of quantum gases in one dimension. After writing a low-energy Hamiltonian, we address the question of localization by considering the pinning of density waves by weak disorder. Using the Renormalization Group and a variationnal method in replica space, we find that the phase diagram is adequately plotted as a function of two parameters: the strength of Bose-Bose and Bose-Fermi interactions. The position and properties of the various phases depend on an additional third parameter, the ratio of the phonon velocities of each component of the gas. Whatever the value of this ratio, we identify -- using the Renormalization Group and a variational calculation -- three types of phases, (i) a fully delocalized phase, that is a two-component Luttinger, (ii) a fully localized phase where both components are pinned by disorder and (iii) an intermediate phase where fermions are localized and bosons are superfluid. The second system is a two-leg ladder lattice of hardcore bosons. Three parameters control the physics: transverse and longitudinal tunneling and the filling. Using several analytical methods (perturbation theory, bosonization, RG) we give an interpretation of new numerical results obtained by our collaborators, namely on the Luttinger parameter of the symmetric mode. We deduce a phase diagram for weak disorder
 
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