Дисертації з теми "Lens spans"
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Grenet, Louis. "Injection de spins dans les semi-conducteurs." Phd thesis, Grenoble, 2010. http://tel.archives-ouvertes.fr/tel-00508923.
Повний текст джерелаForestier, Guillaume. "Transport quantique dans les verres de spins." Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAY023/document.
Повний текст джерелаThe experiments presented in this thesis associate two fields of condensed matter physic, on the one hand with the spin glass physic and the other hand with the mesoscopic physic. The spin glass state is one of the most emblematic of disordered and frustred system and at low temperature, it is caracterized by an unconventionel order where the magnetic disorder is quenched. Moroever, it is considered as a model system for glasses in general and thereby it has been extensively studied, both experimentally and theoreticlly. After extensive research efforts, the description of fundamental state of the system has lead towards two well different approaches. The first, given by the mean field solution, highlights a fundamental composed of mulitple states organised and hierarchical. The second, called droplet model is based on the off--equilibrium dynamic of a unique ground state. However, despite these contributions, the understanding ot this phase is far from being complete and the nature of the ground state still remains an open question. In a mesoscopic conductor, the transport of electron is coherent: electrons keep the memory of their phase, so that one can observe interference effects. The main motivation of this work is to use these interference effects in order to to probe the spin glass state. Indeed, as electronic interference depends of the position of the static disorder, coherent transport can be a useful tool to study the configuration of the microscopic disorder. Althought few coherent transport experiments exist to probe the spin glass, this field of research has very little explored. Nevertheless, this area has been a revival thanks to theoritical work, showing how coherent transport is sensitived to the quenched disorder and how it may provide informations of the nature of fundamental state of spin glass. So, this experimental work deals with the implementation of transport measurements in mesoscopic spin glasses. The first part of the study is focused on the general charateristics of classical and quatum transport of these system. We have examined the resistivity as a function of the temperature and magnetic field and we show that these mesoscopic systems have a spin glass-like behaviour. In a second part, we have focused on the low field magnetoresistivity. We show that it presents a strong hysteresis, whose the amplitude is strongly depends, both of the temperature in the glassy phase and sweeping rate of the magnetic field. We argue that this particular behaviour is related to the out off-equilibrium of the system and we show how the temperature and the sweeping rate control the deviation to the equilibrium. In this part, we also examine by transport measurements how the system relaxes towards the equilibrium just after its excitation. In addition, we present surprinsing transport propreties that we observed, resulting of experimental protocols more sophisticated in temperatures and magnetic fields
PUHA, IOANA. "Frustration et desordre dans les systemes de spins." Paris 11, 2000. http://www.theses.fr/2000PA112159.
Повний текст джерелаLéger, Yoan. "Détection de spins individuels dans les boîtes quantiques magnétiques." Phd thesis, Université Joseph Fourier (Grenoble), 2007. http://tel.archives-ouvertes.fr/tel-00202472.
Повний текст джерелаAubourg, Lucile. "Contrôle et transmission de l'information dans les systèmes de spins." Thesis, Bourgogne Franche-Comté, 2017. http://www.theses.fr/2017UBFCD003/document.
Повний текст джерелаAt an atomic level, the spin control is an essential aim in quantum physics. Unfortunately, the presence of noises disturbs this last. The goal is to find the conditions which we have to impose to the environment in order that the control is not disturbed by the noise. The study of a spin chain characterized by three couplings (Heisenberg, Ising-Z and Ising-X interactions) freely evolving is taken as reference. We observe that the Heisenberg interaction corresponds to an isotropic coupling. The Ising-Z one conserves the order into the chain whereas the Ising-X one is really disordered. We consider a more complex quantum system by adding some control and analyzing its adiabatic behavior. This last is composed by a system and an environment, for which the coupling is perturbative. Three adiabatic regimes have been highlighted. Some formulas allowing to obtain the wave function across the time have been established for these three regimes. However, in practice, quantum systems are not isolated. The interaction with their environment can lead to more complex behaviors, driving the control more difficult. We have studied spin systems, coupled or not, kicked by some ultrashort magnetic pulse trains. These trains cross a classical environment (stationary, drift, Markovian, microcanonical) modifying the strength and the delay of each pulse. The modification of the trains by the environment is one of the sources of the disorder into the spin system. This disorder is transmitted between the spins by the coupling. In this study we do not succeed in controlling the system when the trains are in the presence of the previous environments. To remedy this situation, we force the magnetic pulses to cross a chaotic environment. Before a time t, called horizon of coherence, the system coupled by an Heisenberg interaction and submitted to a chaotic environment remains coherent whereas after, the population and the coherence of one spin and of the average spin of the system tend to go near the microcanonical distribution. During this horizon, it is possible to realize some quantum control either by total control (control of the system at every instants) or by information transmission. This study allows us to determine an empirical formula of the horizon of coherence. Finally, we have tried to find a more formal approach for this horizon
Charpentier, Thibaut. "RMN du solide : des matériaux du nucléaire sous tous les spins." Habilitation à diriger des recherches, Université Pierre et Marie Curie - Paris VI, 2008. http://tel.archives-ouvertes.fr/tel-00345175.
Повний текст джерелаDans un premier chapitre, sont présentées différentes méthodes pour la modélisation et le traitement des spectres RMN MAS et MQMAS de systèmes désordonnés. Nous montrons les possibilités d'extraire les distributions corrélées de paramètres RMN à partir des données expérimentales. Afin de relier ces informations spectrales à des informations structurales, nous décrivons les différentes potentialités offertes par le couplage de calculs ab initio par la méthode GIPAW des grandeurs RMN (Tenseur de déplacement chimique, Gradient local de champ électrique) avec des modélisations de verres par dynamique moléculaires. Des exemples sont présentés sur des systèmes simples SiO2, B2O3 et Na2O-SiO2. Nous montrons l'apport de cette approche RMN premiers principes pour l'amélioration des connaissances sur les relations RMN/structure, l'utilisation de la RMN à validation de modèles structuraux de verres. Des perspectives pour l'incorporation de données RMN dans des approches de modélisation inverse de type Reverse Monte Carlo sont discutées. Si ce type de calculs ab-initio permettent aujourd'hui d'appréhender des systèmes de plusieurs centaines d'atomes, la prédiction du comportement de telles assemblées de spins nucléaires restent néanmoins aujourd'hui encore une difficulté majeure. Nous avons développé une approche théorique pour aborder cette problématique, notamment en présence de rotation de l'échantillon. Son application à des phénomènes d'échange d'aimantation (Ordre dipolaire, Polarisation Croisée) et de phénomènes de relaxation est présentée. Le couplage de ces outils avec les calculs ab-initio devraient permettre d'aborder des question difficiles de la prédiction ab-initio des phénomènes relaxations.
Dans un seconde partie, différentes applications à des problématiques de stockage de déchets nucléaires sont présentées, en soulignant l'apport de la RMN : compréhension des mécanismes d'incorporation dans une matrice hôte cristalline ou vitreuse de terres rares, modifications structurales induites par des agressions interne (effets d'irradiations) ou externes (lixiviation). Phosphates, Silicate de Calcium hydratés, verre borosilicatés (modèles simplifiés des verres nucléaires) sont des matériaux que nous avons étudiés. L'analyse locale qu'apporte la RMN est indispensable pour ces matériaux de compositions complexes et notamment à la compréhension des interactions entre divers éléments : alcalin /alcalino-terreux (Na/Ca), alcalins mixtes (Na/Li,Na/K), effets de substitution. Nous concluons en décrivant les difficultés pour étendre ces études à des matériaux réels, c'est à dire incluant des actinides et/ou produits de fissions : problématique de la RMN MAS sur des échantillons radioactifs; influence du paramagnétisme sur la lisibilité des spectres RMN. Nous présentons les résultats de premières approches pour aborder ces questions.
Lefevre, Alexandre. "États métastables dans les systèmes désordonnés : des verres de spins aux." Phd thesis, Université Paul Sabatier - Toulouse III, 2003. http://tel.archives-ouvertes.fr/tel-00003321.
Повний текст джерелаDans une première partie, les propriétés dynamiques essentielles des modèles de verres de spins en champ-moyen sont passées en revues. La notion d'état métastable est ensuite discutée, ainsi que le lien avec la perte d'ergodicité dans la phase vitreuse. Enfin, plusieurs méthodes numériques et analytiques permettant de calculer l'entropie configurationnelle sont exposées en détail.
La seconde partie traite des états métastables dans les milieux granulaires. Un algorithme de "tapping" y est introduit, permettant d'obtenir un modèle paradigmatique pour l'étude des systèmes granulaires vibrés, partiellement accessible analytiquement. Le scénario proposé par Edwards selon lequel dans l'état stationnaire tous les états métastables sont visités avec la même probabilité est testée sur plusieurs modèles. L'étude de modèles unidimensionnels permet de comprendre la validité de cette approche aux grandes densités, alors que l'étude de modèles sur des graphes aléatoires montre que la mesure d'Edwards permet de décrire de façon précise des phénomènes non triviaux comme des transitions de phase. Enfin, des tests permettant de vérifier expérimentalement cette approche sont proposés.
Bouraoui, Taoufik. "L' impact des spams boursiers sur les caractéristiques des titres financiers." Paris 10, 2009. http://www.theses.fr/2009PA100121.
Повний текст джерелаLaunched for the first time on a scam that promised to obtain work permits for immigrants in USA, spam has evolved from drugs,false diplomas, phishing. . . Until the appearance of messages that are intented to manipulate stock prices. These messages,called stock spams based on the following principle : spammers start by buying gradually, for not raising the price, a large quantity of securities. Then, by messages taking the form of financial advice, they arouse interest for the stock objet of spam, in order to increase artificially prices. Finally, once the price reaches the desired level, they sell all the stocks and make profits. The constant increase of stock spams does not any more allow considering these phenomena as negligible and leads to wonder about effects which they can have on the dynamics of stock prices. We therefore proposed in this thesis to study the impact of stock spams on three variables namely volume,return and volatility. The implementation of the event study methodology showed that these messages have a significant impact on the activity of penny stock market. This market is illiquid and we cannot exclude that abnormal variations are largely dependent on the degree of illiquidity of each security. To check this assumption, we used a regression model in order to determine whether the variable of illiquidity measured by the Amihud ratio has an explanatory power on the abnormal reaction of volume, return or volatility. Our results have highlighted a significant relationship between illiquidity and the reactions of each of the three variables. Therefore, the significant effect observed on the characteristics of penny stock securities is due to their lack of liquidity
GROLLAU, SYLVAIN. "Une approche thermodynamiquement coherente pour les modeles de spins classiques tridimensionnels." Paris 11, 2001. http://www.theses.fr/2001PA112112.
Повний текст джерелаCépas, Olivier. "Effets des anisotropies de spins dans les oxydes de basse dimension." Université Joseph Fourier (Grenoble), 2000. http://www.theses.fr/2000GRE10193.
Повний текст джерелаWendenbaum, Pierre. "Intrication et dynamique de trempe dans les chaînes de spins quantiques." Thesis, Université de Lorraine, 2014. http://www.theses.fr/2014LORR0170/document.
Повний текст джерелаThe study carried in this thesis concerns the dynamics of out-Of-Equilibrium quantum systems, and more particularly their entanglement properties. Indeed, entanglement became a fundamental concept in modern physics, especially with the development of quantum information. We have in a first part studied the dynamics of a model of bosons on a lattice after the quench of their trapping potential. In the hard-Core limit, we developed an hydrodynamical theory which perfectly reproduced the observed behavior. Then, we have looked at the dynamics of two defect spins coupled to an Ising chain. When these defects have been prepared into a separable state, we have established a formula giving the evolution of the reduced density matrix, allowing us to have access to the entanglement create through the coupling to the chain. We considered then the case of two initially entangled defect spins, and we studied the influence of a non-Equilibrium environment on the disentanglement properties. Finally, the last part of this thesis is devoted to the study of a system coupled to an environment by means of the repeated interactions process. We studied the relaxation of the system in two different time regimes. For short times, the state is well described by a non-Equilibrium-Steady-State, in which we highlighted the scaling properties of some observables. For long times, the system reaches an equilibrium steady state made of a product of Bell states
Lavarelo, Arthur. "De la frustration et du désordre dans les chaînes et les échelles de spins quantiques." Phd thesis, Université Paris Sud - Paris XI, 2013. http://tel.archives-ouvertes.fr/tel-00923197.
Повний текст джерелаBENAKLI, MOURAD. "Influence du desordre sur les symetries discretes dans les systemes de spins xy completement frustres." Paris 11, 1995. http://www.theses.fr/1995PA112328.
Повний текст джерелаGauthé, Olivier. "Méthodes de réseaux de tenseurs pour les systèmes de spins SU(N)." Thesis, Toulouse 3, 2019. http://www.theses.fr/2019TOU30279.
Повний текст джерелаThe study of strongly correlated electron systems is one of the most challenging target of modern condensed matter physics. Beyond the Mott transition, these systems are magnetic insulators that can be described by a spin wavefunction. This concept can be generalized by replacing the spin variable by an irreducible representation of the group SU(N), which is relevant in some cold atomic gases experiments. This thesis aims to determine the physical properties of paradigmatic wavefunctions of condensed matter systems ruled by SU(N) symmetry using tensor network algorithms. These methods have already proven to be efficient to tackle problems with discrete variables on a lattice. Here, the formalism of Projected Entangled Pair States (PEPS) is used to design elementary tensors with intrinsic SU(N) symmetry that describe quantum spin liquid phases. This method is first applied to the generalization to SU(3) symmetry group and in two dimensions on the square lattice of the Affleck-Kennedy-Lieb-Tasaki (AKLT) wavefunction. It is shown to belong to the class of symmetry protected topological phases. Subsequently, the generalization to SU(N) of resonant valence bond (RVB)-like states on the square lattice is investigated, first for staggered fundamental-conjugate representations. A system of two SU(4) fermions per site is then considered and described with generalized RVB wavefunctions. These states are shown to represent a Z2 topological quantum spin liquid, possibly chiral, that does not break any spatial symmetry. A reasonable, short-range Hamiltonian able to stabilize this phase is proposed
Laversanne, René. "Localisation électronique et mise en ordre des spins dans les conducteurs organiques." Bordeaux 1, 1987. http://www.theses.fr/1987BOR10506.
Повний текст джерелаLaversanne, René. "Localisation électronique et mise en ordre des spins dans les conducteurs organiques." Grenoble 2 : ANRT, 1987. http://catalogue.bnf.fr/ark:/12148/cb376070780.
Повний текст джерелаBourges, Philippe. "DYNAMIQUE DE SPINS DANS LES OXYDES DE CUIVRE SUPRACONDUCTEURS A HAUTE TEMPÉRATURE CRITIQUE." Habilitation à diriger des recherches, Université Paris Sud - Paris XI, 2003. http://tel.archives-ouvertes.fr/tel-00003467.
Повний текст джерелаLefevre, Alexandre. "Etats métastables dans les systèmes vitreux : des verres de spins aux milieux granulaires." Toulouse 3, 2003. http://www.theses.fr/2003TOU30070.
Повний текст джерелаClément, Thomas. "Etude par spectroscopie optique de la dynamique de spins dans les nanostructures CdMnTe." Université Joseph Fourier (Grenoble), 2009. http://www.theses.fr/2009GRE10108.
Повний текст джерелаWe studied Mn spin dynamics in II-VI magnetic quantum wells and quantum dots and we showed the complex dynamics ofthese Mn is driven bl their coupling to different solid excitations. The environment importance has been investigated while varyirig the studied structures dimensionality, thej Mn concentration or the applied magnetic field. We demonstrate that depending on these variables values, the coupling of one of the solid excitations with the Mn generally overcomes the other ones. Thanks to magneto-optical micro-spectroscopic studies of magnetic quantum dots, we first proved the influence ofphotocreated carriers in the vicinity of quantum dots over the Mn dynamics. These carriers induce a heating effect due to a flip-flop mechanism between carriers and Mn, and controlled by a positive feedback loop. Moreover, this effect is all the more important than magnetic field ane Mn concentration are low and than system dimensions are small. Then, the experimental development ofa "high" pulsed magnetic field technique allowed us to optically probe the Mn dynamics in magnetic quantum wells. This results in the observation of a very fast Mn dynamics, under zero or low magnetic field, and for low Mn concentration. This dynamics, not well understood yet, seems to be due to the evolution, during the field pulse, of isolated Mn whose internai energetic structure is complex because ofhyperfme interaction and strains
Allen, Dave. "Étude des chaînes de spins par les méthodes de la théorie quantique des champs." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0004/NQ40506.pdf.
Повний текст джерелаDargis, Pierre. "Structures non-locales dans les systèmes intégrables, systèmes KdV supersymétriques et chaînes de spins." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape9/PQDD_0005/NQ39345.pdf.
Повний текст джерелаAllen, Dave. "Étude des chaînes de spins par les méthodes de la théorie quantique des champs." Sherbrooke : Université de Sherbrooke, 1998.
Знайти повний текст джерелаBouzerar, Richard. "Théorie pour les systèmes désordonnés de spins localisés en interaction avec des porteurs itinérants : les semiconducteurs magnétiques dilués." Phd thesis, Université de Picardie Jules Verne, 2008. http://tel.archives-ouvertes.fr/tel-00367282.
Повний текст джерелаVallejo, Castaneda Emmanuel. "Contribution à l'étude de l'ordre de spins, de charge et effets structuraux dans le modèle de double-échange : chaîne linéaire, échelles de spins et manganites." Phd thesis, Université Joseph Fourier (Grenoble), 2006. http://tel.archives-ouvertes.fr/tel-00086637.
Повний текст джерелаBailleul, Matthieu. "Propagation et confinement d'ondes de spin dans les microstructures magnétiques." Phd thesis, Ecole Polytechnique X, 2002. http://tel.archives-ouvertes.fr/tel-00001976.
Повний текст джерелаhaute fréquence (GHz). Dans ce but, un spectromètre hyperfréquence à antennes micrométriques a été mis au point. Cet
instrument a été utilisé pour explorer deux problématiques différentes. Pour un film continu, d'abord, nous avons réalisé des
expériences d'émission-réception d'ondes de spin. Ces résultats nous ont permis de caractériser les processus de
transduction et de relaxation d'ondes magnétostatiques progressives. Nous avons également étudié des rubans de largeur
micrométrique, pour lesquels l'équilibre lui-même est inhomogène. Nous avons interprété leur réponse hyperfréquence en
termes de transitions de phase micromagnétiques et en termes de confinement d'ondes de spin.
REYNAL, SYLVAIN. "Transitions de phase dans les systèmes de spins régis par des interactions à longue portée." Phd thesis, Université de Cergy Pontoise, 2005. http://tel.archives-ouvertes.fr/tel-00010256.
Повний текст джерелаXudous, Yorgo. "Structure des lois de conservation dans les chaînes de spins avec interactions à longue portée." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/MQ38212.pdf.
Повний текст джерелаMaucourt, Jérôme. "Étude par simulations numériques des transitions de phase dans les modèles de spins XY désordonnés." Université Joseph Fourier (Grenoble ; 1971-2015), 1997. http://www.theses.fr/1997GRE10216.
Повний текст джерелаPlacial, Jean-Pierre. "Étude d’états multiple dans les protéines par Résonance Magnétique Nucléaire : Méthodologie du traitement des données de dispersion de relaxation." Paris 6, 2013. http://www.theses.fr/2013PA066754.
Повний текст джерелаThis thesis deals with the identification of a new source of error concerning the treatment of data acquired with relaxation dispersion experiments. This method may be used to characterize conformational exchange in proteins and is based on the chemical exchange of nuclei between different electronic environments during a series of spin echoes. The source of error was identified through the study of spin dynamics. Its come from the simultaneous use of two approximations: the description of magnetization’s evolution with a single relaxation constant and the use of an intensity recorded without spin echoes as reference to estimate this constant. This can significantly distort the relaxation dispersion curves and thus provoke an inaccurate treatment. A script was written for an accurate treatment, which take into account the identified source of error. Relaxation dispersion of amid nitrogen and proton were performed on two proteins: the domain 1 of human annexin 1 and the small G protein Arf1. The data were treated with the script
Jbeli, Anouar. "Dynamique de photoluminescence dans les boîtes quantiques auto-assemblées InGaAs/GaAs : propriétés de spin et couplage électronique inter-boîte." Toulouse, INSA, 2003. http://www.theses.fr/2003ISAT0015.
Повний текст джерелаBonzom, Valentin. "Géométrie quantique dans les mousses de Spins : de la théorie topologique BF vers la relativité générale." Thesis, Aix-Marseille 2, 2010. http://www.theses.fr/2010AIX22072/document.
Повний текст джерелаLoop quantum gravity has provided us with a canonical framework especially devised for back-ground independent and diffeomorphism invariant gauge field theories. In this quantization the funda-mental excitations are called spin network states, and in the context of general relativity, they give ameaning to quantum geometry. Spin foams are a sort of path integral for spin network states, supposed to enable the computations of transition amplitudes between these states. The spin foam quantization has proved very efficient for topological field theories, like 2d Yang-Mills, 3d gravity or BF theories. Different models have also been proposed for 4-dimensional quantum gravity.In this PhD manuscript, I discuss several methods to study spin foam models. In particular, I present some recurrence relations on spin foam amplitudes, which generically encode classical symme-tries at the quantum level, and are likely to help fill the gap with the Hamiltonian constraints. These relations can be naturally interpreted in terms of elementary deformations of discrete geometric struc-tures, like simplicial geometries. Another interesting method consists in exploring the way spin foam models can be written as path integrals for systems of geometries on a lattice, taking inspiration from topological models and Regge calculus. This leads to a very geometric view on spin foams, and gives classical action principles which are studied in details
Orain, Jean-Christophe. "Frustration géométrique et nouveaux états quantiques de spins dans les composés vanadates fluorés à géométrie kagomé." Thesis, Université Paris-Saclay (ComUE), 2015. http://www.theses.fr/2015SACLS113/document.
Повний текст джерелаThe search for quantum liquid state is a very active field in condensed matter research. In two dimensions, the antiferromagnetic spin 1/2 kagome lattice seems to be the most able to stabilize such a ground state. Indeed, from recent theoretical investigations, we are now quite sure that this model has a quantum spin liquid ground state. However, we still do not know its nature, in particular the nature of its correlations. They could be short ranged with a gap in the excitation spectrum, or long ranged with a gapless excitation spectrum. On the experimental side, only few materials exist and only one possesses a geometrically perfect lattice, the Herbertsmithite. All the experiments that have been done on this compound reveal a gapless spin liquid state along with deviations to the spin 1/2 Heisenberg hamiltonian which could be responsible of the gap closure.This thesis deals with the experimental study, mainly by NMR and µSR, of new vanadium based kagomé compounds which are part of a newly synthesized family, the kagome fluoride vanadates. The material that we studied the most is a spin 1/2 kagomé compound based on V4+, (NH4)2[C7H14N][V7O6F18] (DQVOF). The magnetic model of this compound can be decomposed in two rather independent parts, trimerized kagome planes and quasi paramagnetic V3+ ions. The µSR studies, showing the absence of frozen moment down to 20 mK, reveal a spin liquid ground state in DQVOF. The heat capacity and the NMR experiments point out a gapless behavior despite trimerization and likely weak Dzyaloshinskii Moriya interactions. Our results demonstrate that the gapless ground state, whether intrinsic or due to deviation to the ideal hamiltonian, is a rather robust characteristic of kagome materials.Furthermore, we studied another compound of this family, (NH4)2[C2H8N][V3F12] (DDVF), which magnetic lattice is made of uncoupled kagomé planes based on V3+ (S = 1). The lattice shows large deviations to the ideal kagomé and the thermodynamic experiments and the µSR studies reveal a magnetic transition to a frozen state at 10 K with a long distance order which is effective only below 6 K
Dumazy, Yves. "Les échos quadrupolaires : optimisation et applications à la caractérisation de composés à base de sodium, de cuivre et de niobium." Lille 1, 1997. http://www.theses.fr/1997LIL10125.
Повний текст джерелаLes différentes parties qui composent le fid après la seconde impulsion (échos, anti-échos et transitoires) sont déduits du calcul des conditions de refocalisation. Utilisant le concept de chemin de transfert de cohérence dans la matrice densité, nous montrons que la refocalisation complète du signal d'écho, pour les interactions au 1#e#r et 2#n#d ordre, correspond aux éléments monoquanta (1q), crées pendant la première impulsion, et transfères vers les termes -1q par la seconde impulsion. Les autres cohérences provoquent des distorsions qu'il faut éliminer en jouant sur les paramètres expérimentaux de la séquence. Enfin, nous montrons que ces bonnes conditions expérimentales conduisent a la détermination des paramètres caractéristiques des interactions a partir de la forme de raie sur plusieurs composes
Kober-Lehouelleur, Pascale. "Inhomogénéités magnétiques dans les manganites La1-xCaxMnO3 et La1-xSrxMnO3, (0." Paris 11, 2004. http://www.theses.fr/2004PA112174.
Повний текст джерелаThe aim of this work is the study of the static and dynamical properties of the La(1-x)Ca(x)MnO(3) and La(1-x)Sr(x)MnO(3) compounds for x<0. 3. At low temperature, an insulating canted antiferromagnetic phase is observed for 00. 22, these compounds become ferromagnetic and metallic. In the canted antiferromagnetic phase, diffuse neutrons scattering evidenced small anisotropic ferromagnetic inhomogeneities, rather holes-rich leading to a picture ofmodulated canted state. The study of this modulated canted state under magnetic field allows us to determine the nature of the two measured spin-waves branches. They are attributed to two strongly coupled ferromagnetic and antiferromagnetic components. In the next phase, the spin wave dispersion split into several dispersionless or weakly-dispersed branches. We interpret these levels by the presence of confined spin-waves in small ferromagnetics clusters, rather holes-poor. These clusters evolve with doping. They are bidimentionnal, with a size of 16 Angstroms, for the Ca 17 % compound and isotropic, with a size of 8 Angstroms, for the Ca 20 % compound. This study allows us to understand precisely the rôle of magnetic inhomogeneities and charge segregation in the mechanism that brings to the metal/insulator transition at x=0. 22
Léguillon, Romain. "Triaxialité et isomèrisme à hauts spins dans les noyaux proches de la fermeture de couche N = 82." Phd thesis, Université Paris Sud - Paris XI, 2013. http://tel.archives-ouvertes.fr/tel-00932123.
Повний текст джерелаCamara, Ibrahima Sock. "Étude, par Résonance de Spin Électronique, de la dynamique des spins dans les composés à base de dimères de spins 1/2, CsV2O5, VO(HPO4)*0.5H2O et KZn(H2O)(VO)2(PO4)2(H2PO4)." Phd thesis, Aix-Marseille Université, 2012. http://tel.archives-ouvertes.fr/tel-00747670.
Повний текст джерелаBAYONG, EMILIENNE. "Etude des phenomenes critiques dans les systemes de spins avec des interactions a longue portee par les methodes de simulation numerique de monte-carlo." Cergy-Pontoise, 1999. http://www.theses.fr/1999CERG0069.
Повний текст джерелаChafai, Djalil. "Sur les inégalités de Sobolev logarithmiques en théorie de l'information et pour des systèmes de spins conservatifs en mécanique statistique." Phd thesis, Université Paul Sabatier - Toulouse III, 2002. http://tel.archives-ouvertes.fr/tel-00001382.
Повний текст джерела2°) Etude de l'inégalité de Sobolev logarithmique en théorie de l'information.
3°) Etablissement d'inégalités de Poincaré et de Sobolev logarithmiques pour certaines dynamiques de Kawasaki et Glauber pour un modèle à spins continus en mécanique statistique.
Tribollet, Jérôme. "Dynamique des spins électroniques et excitoniques dans les hétérostructures semiconductrices 2D et 0D mesurée par rotation Faraday résolue en temps." Paris 7, 2003. http://www.theses.fr/2003PA077121.
Повний текст джерелаAtas, Yasar Yilmaz. "Quelques aspects du chaos quantique dans les systèmes de N-corps en interaction : chaînes de spins quantiques et matrices aléatoires." Thesis, Paris 11, 2014. http://www.theses.fr/2014PA112221/document.
Повний текст джерелаMy thesis is devoted to the study of some aspects of many body quantum interacting systems. In particular we focus on quantum spin chains. I have studied several aspects of quantum spin chains, from both numerical and analytical perspectives. I addressed especially questions related to the structure of eigenfunctions, the level densities and the spectral properties of spin chain Hamiltonians. In this thesis, I first present the basic numerical techniques used for the computation of eigenvalues and eigenvectors of spin chain Hamiltonians. Level densities of quantum models are important and simple quantities that allow to characterize spectral properties of systems with large number of degrees of freedom. It is well known that the level densities of most integrable models tend to the Gaussian in the thermodynamic limit. However, it appears that in certain limits of coupling of the spin chain to the magnetic field and for finite number of spins on the chain, one observes peaks in the level density. I will show that the knowledge of the first two moments of the Hamiltonian in the degenerate subspace associated with each peak give a good approximation to the level density. Next, I study the statistical properties of the eigenvalues of spin chain Hamiltonians. One of the main achievements in the study of the spectral statistics of quantum complex systems concerns the universal behaviour of the fluctuation of measure such as the distribution of spacing between two consecutive eigenvalues. These fluctuations are very well described by the theory of random matrices but the comparison with the theoretical prediction generally requires a transformation of the spectrum of the Hamiltonian called the unfolding procedure. For many-body quantum systems, the size of the Hilbert space generally grows exponentially with the number of particles leading to a lack of data to make a proper statistical study. These constraints have led to the introduction of a new measure free of the unfolding procedure and based on the ratio of consecutive level spacings rather than the spacings themselves. This measure is independant of the local level density. By following the Wigner surmise for the computation of the level spacing distribution, I obtained approximation for the distribution of the ratio of consecutive level spacings by analyzing random 3x3 matrices for the three canonical ensembles. The prediction are compared with numerical results showing excellent agreement. Finally, I investigate eigenfunction statistics of some canonical spin-chain Hamiltonians. Eigenfunctions together with the energy spectrum are the fundamental objects of quantum systems: their structure is quite complicated and not well understood. Due to the exponential growth of the size of the Hilbert space, the study of eigenfunctions is a very difficult task from both analytical and numerical points of view. I demonstrate that the groundstate eigenfunctions of all canonical models of spin chain are multifractal, by computing numerically the Rényi entropy and extrapolating it to obtain the multifractal dimensions
Eble, Benoit. "Interaction hyperfine dans les boîtes quantiques d'InAs/GaAs sous pompage optique orienté." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2006. http://tel.archives-ouvertes.fr/tel-00197618.
Повний текст джерелаCelle-ci, équivalente pour le spin électronique µa un champ magnétique aléatoire de quelques dizaines de mT d'amplitude, est à l'origine d'un mécanisme de déphasage en un temps de l'ordre de la nanoseconde.
Ce travail de thèse mets en lumière le rôle fondamental joué par ce couplage hyperfin lors des expériences d'orientation optique des porteurs dans des boîtes quantiques InAs dont la charge est contrôlée par une tension de grille. La spectroscopie haute résolution de la photoluminescence de boîtes uniques, ainsi que des mesures sur ensemble, résolues en temps ou en présence d'un champ magnétique, permettent de dresser un panorama assez complet. En particulier, la polarisation dynamique des noyaux et la relaxation de spin induite par l'interaction hyperfine apparaissent comme deux manifestations majeures et antagonistes du couplage hyperfin intrinsèques au système "électron-noyaux".
Dominiczak, Maguy Ruyter Antoine. "Etude de la séparation de phase et polarisation de spins dans les manganites La0.8Sr0.2MnO3 par microscopie en champ proche et magnétotransport." Tours : SCD de l'université de Tours, 2008. http://www.applis.univ-tours.fr/theses/priv/maguy.dominiczak_2772.pdf.
Повний текст джерелаDominiczak, Maguy. "Etude de la séparation de phase et polarisation de spins dans les manganites La0.8Sr0.2MnO3 par microscopie en champ proche et magnétotransport." Thesis, Tours, 2008. http://www.theses.fr/2008TOUR4028.
Повний текст джерелаPerovskite manganite compounds are potential candidates for magnetic and magnetoresistive applications. They have known a resurge in interest during the last ten years and the growth of single crystals has become necessary to better understand and improve the study of the physical properties carried out on thin films of the same composition. In the present work, we were quite particularly interested in the La0.8Sr0.2MnO3 compound elaborated in an image furnace by the floating zone technique. Its most exciting properties can in fact be studied at room temperature. The structural and textural parameters were analyzed by near field microscopy, as well as by scanning and transmission microscopy. We were thus able to observe twins on the surface of all samples and also amorphous defects of nanometric size, but no grain boundaries were found. Concentrated mainly in the central part of the material, these modify the magnetic interactions between domains. On the other hand, near the edges, as the crystal structure is better maintained, the magnetic coupling is stronger. An ordering of the magnetic domains could be found, along an axis of easy magnetization. In transport, experiments non-linear effects due to Joule heating were observed in the alternating current regime. Having established in which range of current values the response was linear, the intrinsic properties of the La0.8Sr0.2MnO3 single crystals were studied, for example, relaxation phenomena of the resistance at room temperature. By measuring the spreading resistance, the phase coexistence between metallic clusters and an insulating matrix was revealed. This allows us to interpret our transport measurements in terms of percolation of ferrometallic domains. To finish, in the direct current regime, we show that, near the Curie point, the conduction electrons, spin-polarized according to the magnetization direction of hard ferromagnetic domains, flip, under the influence of a magnetic torque, the moments of soft ferromagnetic domains in a continuous and reversible way, being able thereby to lead to an enhancement of up to 30 % of the magnetization in the material
Villar, Arribi Pablo. "Fermions lourds et métaux de Hund dans les supraconducteurs à base de fer." Thesis, Université Grenoble Alpes (ComUE), 2018. http://www.theses.fr/2018GREAY070/document.
Повний текст джерелаMaterials where the electrons responsible for the low-energy properties experience strong correlations are today very investigated in search of emerging new phases with surprising and/or useful properties. Iron-based superconductors (IBSC) are now considered in this class of compounds. Using the many-body techniques necessary for the theoretical treatment of these correlations (slave-spin mean field theory - SSMFT- and dynamical mean field theory - DMFT- in conjunction with density functional theory, DFT), in this thesis I address several properties of IBSC.First I analyze the very hole-doped compounds in the IBSC family, that show experimentally some behaviors typical of the so-called “heavy fermions”, compounds typically of rare earth or actinides, where extremely correlated electrons coexist with others less correlated. In particular I focus on the specific heat and the thermoelectric power and show how these properties can be understood in the recently developed paradigm of “Hund’s metals”. Indeed the intra-atomic exchange (the “Hund’s coupling”) is responsible for these materials of transition metal elements showing heavy-fermionic physics. I show also that typical heavy-fermionic features of the excitation spectrum, known as Van Hove singularities are well captured by our modelization within DFT+SSMFT. I then use DMFT in a model in order to study the direct impact of the Van Hove singularities on the strength of correlations.In a second part I show how FeSe, the presently most studied IBSC, is also in a Hund’s metal phase, but it is brought to the frontier of this phase by pressure. This frontier is connected to an enhancement of the electronic compressibility which correlates positively then with the enhancement of superconductivity found in experiments. I perform an analogous study on the record holder for the highest critical superconducting temperature, the monolayer FeSe where I also find an enhanced compressibility. This supports the recent proposal that the frontier of a Hund's metal favors high-temperature superconductivity.Finally I study the nature of magnetism in another family of IBSC, the iron-germanides. I explore different possible magnetic orders with DFT simulations and study their competition (which can in principle favor superconductivity) in several compounds where different chemical substitutions are applied to the parent compound YFe2Ge2. I also study the effect of chemical pressure on this compound
Domenge, Jean-Christophe. "Brisures de symétrie dans les modèles de Heisenberg classiques et quantiques en deux dimensions." Paris 6, 2005. https://tel.archives-ouvertes.fr/tel-00010943.
Повний текст джерелаRulquin, Charlotte. "Rôle des fluctuations dans les systèmes vitreux de dimension finie." Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066454/document.
Повний текст джерелаWhen the temperature diminishes, glassy systems present a very sluggish dynamics and at low enough temperature can finish in some arrested disordered state. This thesis deals about the case of structural glasses, to which category supercooled liquids belong to, and spin glasses.In these two cases the physical scenarios issued from the mean-field theories are known and could be fragile to the introduction of fluctuations that are present in finite-dimensional systems. Since the study of the effect of fluctuations in glassy systems is a daunting task, the aim of this thesis is to study simple related problems in which the effect of fluctuations can be thoroughly investigated.For the structural-glass case, we study first the return to convexity of the free energy of a uni-dimensional finite-size system where fluctuations are restricted by the finite size of the system. Then, we study the role of "short"- and "long"-range fluctuations in a glass-former model called ``plaquette model'' in comparing the thermodynamic properties of the system which are known on Euclidean lattices with the ones we obtained on a "tree" lattice. Finally, we study the existence of space-time fluctuations in a model made of activated-dynamics systems coupled via a thermal bath at low temperature.For the spin-glass case, we construct a scheme for the nonperturbative renormalization group to describe the effect of critical fluctuations on the critical properties of the Ising spin glass in zero field in dimensions lower than six
De, person Pierre. "Jonctions tunnel à aimantation perpendiculaire : croissance, caractérisations structurales ; phénomènes de couplage, magnétotransport ; extension aux hétérostructures pour l'injection de spins dans les semiconducteurs III-V." Université Joseph Fourier (Grenoble), 2007. http://www.theses.fr/2007GRE10035.
Повний текст джерелаThe subject of this thesis is the elaboration by epitaxy and the characterization of devices designed for spintronic applications : magnetic tunnel junctions (FePt/MgO/FePt) and hybrid heterostructures ferromagnetic metal / semiconductor III-V (FePt/MgO/GaAs). Ln both cases we used MgO as an insulating barrier and FePt ferromagnetic electrodes with magnetization perpendicular to the surface plane (the L1o ordered alloy). This ferromagnetic material has been chosen for the purpose of creating future magnetic memories because its large anisotropy enables a stable magnetic information. Different magnetic behaviors have been shown for each of the two electrodes of the magnetic tunnel junctions. Structural characterizations of the system performed during the growth process led us to attribute this effect to the epitaxial strain of the thin films. Surprisingly at first sight, the magnetic decoupling of the system is not guaranteed in the general case because of the strong magnetization of the ferromagnetic layers that induces a strong stray field during the magnetization reversaIs. We also were able to deduce, by experiments and calculations, the influence of the thickness of the electrodes on the general magnetic properties of the device. Studies of magnetization reversaI dynamics have shed some light on the key role played by the pinning of the domain walls during the magnetization reversals. All-epitaxial FePtlMgO/GaAs hybrid systems were elaborated by combining different deposition chambers. We managed to grow systems exhibiting very good structural and magnetic properties
Sanquer, Marc. "Transport électronique et magnétisme dans les conducteurs organiques irradiés." Paris 11, 1985. http://www.theses.fr/1985PA112321.
Повний текст джерелаZerrouki, Thileli. "Triaxialité et coexistence de forme dans les noyaux proches de la fermeture de couche N = 82 : évolution de forme et rotation magnétique dans ¹⁴¹Nd." Thesis, Paris 11, 2015. http://www.theses.fr/2015PA112069/document.
Повний текст джерелаThis PhD work was devoted to the study of exotic nuclear rotation and stable triaxiality at very high spin. In, nuclei with a few holes in the N = 82 shell closure, which exhibit a large variety of excitations at medium and high spins. The peculiar feature of these nuclei is the existence of coexisting shapes, spherical and triaxial, up to very high spins.During my PhD I analyzed an experiment performed with the Euroball multidetector at IPHC (Strasbourg) for the study of high-spin states in ¹⁴¹Nd populated using the ⁹⁶Zr (⁴⁸Ca, 3n) fusion-evaporation reaction. We have identified several high-spin bands and developed the level scheme up to an excitation energy and spin of 19 MeV and 81/2⁻ , respectively, which are much higher than previously published (9.4 MeV and 49⁄2 ℏ). Three new dipole bands and three new ΔI = 2 rotational bands have been identified. The main yrast sequence was extended up to spin 61/2⁻.A detailed interpretation of the observed bands was performed, for the first time, using theoretical calculations with Cranked Nilsson-Strutinsky (CNS) and the Tilted Axis Cranking (TAC) models. A consistent interpretation of most of the observed bands was realized. They appear to be based on nearly spherical for the main sequence, slightly deformed for the dipole bands and triaxially deformed minima for the ΔI = 2 bands. The observed level structure of ¹⁴¹Nd reveals the capability of the nuclei with a few holes in the N = 82 shell closure to acquire different shapes and to rotate around a principal or a tilted axis relative to the intrinsic reference system, as in the case of the ¹³⁸Nd and ¹⁴⁰Nd nuclei recently studied by our group
Abergel, Daniel. "Nouveaux aspects methodologiques en rmn des proteines : aspects theoriques de l'amortissement par rayonnement coherent et: recherches sur le probleme de l'extraction automatique des systemes de spins dans les experiences de rmn 3d." Paris 11, 1994. http://www.theses.fr/1994PA112240.
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