Dissertations / Theses on the topic 'Fermion interactions'
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Thornton, Andrew M. "Studies of lattice fermion-scalar interactions." Thesis, University of Edinburgh, 1989. http://hdl.handle.net/1842/14539.
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Shively, William F. Khveshchenko D. V. "Novel behaviors in fermion systems with point-like Fermi surfaces and singular interactions." Chapel Hill, N.C. : University of North Carolina at Chapel Hill, 2006. http://dc.lib.unc.edu/u?/etd,439.
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Thesis (Ph. D.)--University of North Carolina at Chapel Hill, 2006.Title from electronic title page (viewed Oct. 10, 2007). "... in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Physics & Astronomy." Discipline: Physics and Astronomy; Department/School: Physics and Astronomy.
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Karim, Pour Farshid. "Quantum Monte Carlo studies of fermions with attractive interactions in optical traps." [S.l. : s.n.], 2008. http://nbn-resolving.de/urn:nbn:de:bsz:93-opus-34763.
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Fraser, Louisa Mairi. "Coulomb interactions and positron annihilation in many fermion systems : a Monte Carlo approach." Thesis, Imperial College London, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.338685.
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Curtis, Duncan Charles. "A non-perturbative study of fermion propagators and their interactions in gauge theories." Thesis, Durham University, 1991. http://etheses.dur.ac.uk/6275/.
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In this thesis we study the non-perturbative behaviour of the fermion propagator in an Abelian gauge theory, namely four dimensional, quenched QED –where by quenched we mean that we neglect the effect of the fermion loops in the boson propagator. What is of primary interest is the dynamical generation of mass. In order to carry out this study we need to make use of the Schwinger-Dyson equations, which are the field equations of the theory. For the investigation of the fermion propagator, the form of the three point interaction is of critical importance. We study the usual ansatz, the Ball-Chiu form, for the three point function, that is obtained from the Ward-Takahashi identities, and improve upon it. This is done by making use of the powerful constraints that Multiplicative Renormalizability place upon the theory in the perturbative (high energy) region. We initially study the theory in the massless case, for simplicity, where we find that using our improved ansatz we can obtain an exact, non-perturbative solution for the renormalised wave function. Moving on, we then study the theory in the massive case -where we have a brief interlude to look at the ladder approximation. We solve the theory in the case where there is a finite cutoff and reproduce the well-known critical coupling point. We then consider the case where there is an infinite cutoff, when we find no critical coupling. We discuss and explain the differences. Returning to our improved ansatz for the fermion-boson vertex we solve the renormalised theory for both the wavefunction and mass function and find that there is no critical coupling. In doing this having a form for the fermion-boson vertex that satisfies both the Ward-Takahashi identity and Multiplicative Renormalizability is essential. These studies suggest that full QED may turn out to be a theory without a critical coupling and thus be free of phase changes.
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Pfoh, Torsten [Verfasser]. "Electroweak precision observables and effective four-fermion interactions in warped extra dimensions / Torsten Pfoh." Mainz : Universitätsbibliothek Mainz, 2011. http://d-nb.info/1026802652/34.
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Howald, Ludovic. "Interactions entre la supraconductivité et la criticité quantique, dans les composés CeCoIn5, URhGe et UCoGe." Phd thesis, Université de Grenoble, 2011. http://tel.archives-ouvertes.fr/tel-00584598.
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Le sujet de cette thèse est l'analyse du second champ critique supraconducteur (Hc2) ainsi que l'interaction entre la supraconductivité et les points critiques quantiques (PCQ), pour les composés CeCoIn5, URhGe et UCoGe. Dans le composé CeCoIn5, l'étude par résistivité du domaine de liquide de Fermi a permis la localisation précise du PCQ a pression ambiante. Cette analyse permet d'invalider l'hypothèse d'une coïncidence entre Hc2(0) et le PCQ. Dans une deuxième partie, l'évolution sous pression de Hc2 est analysée. Le dôme supraconducteur de ce composé est non-conventionnel avec deux pressions caractéristiques différentes: à ~1.6GPa, la température de transition supraconductrice est maximum alors que c'est à ~0.4GPa que la plupart des grandeurs physiques (maximum de Hc2(0), maximum de la pente dHc2/dT, maximum du saut de chaleur spécifique DC/C, ...) suggèrent la présence d'un PCQ. Nous expliquons cet antagonisme par l'importance des processus de brisure de pairs liés a la proximité du PCQ. Ces deux observations nous permettent de proposer un nouveau diagramme de phase pour CeCoIn5. Dans une troisième partie, les mesures de conduction thermique sur les composés URhGe et UCoGe sont présentées. Elles nous permettent dans un premier temps d'obtenir la transition "bulk" supraconductrice et de confirmer la forme in-habituelle de Hc2 observée en résistivité. La dépendance en températures et en champs de la conduction thermique nous permet d'identifier une contribution non-électronique au transport de chaleur jusqu'aux plus basses températures. D'autre part, nous identifions deux différents domaines supraconducteurs a bas et hauts champs appliqués selon l'axe b. Ces deux domaines sont compatibles avec un modèle de supraconductivité multigaps. Suivant ces observations et des mesures de pouvoir thermoélectrique, nous proposons un modèle de transition de Lifshitz pour ces deux composés.
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Baez, Michael Cabrera. "Fundamental electronic and magnetic interactions in the cage compounds RT2Zn20 (R = Y, Gd, Yb, T = Fe, Co)." reponame:Repositório Institucional da UFABC, 2017.
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Orientador: Prof. Dr. Marcos Abreu AvilaTese (doutorado) - Universidade Federal do ABC, Programa de Pós-Graduação em Física, 2017.
The electronic correlations originated from the Coulomb interactions between electrons play a fundamental role in the establishment of the physical properties of a wide range of materials. For the case of weak correlations, the material can be described within a simplied non-interacting point of view, as in the case of standard metals. Unexpected and intriguing properties are revealed when strong correlations are involved, due to a large number of degrees of freedom in the electronic correlations. As a result of this electronic correlation, it is possible to go from conventional forms of magnetism, passing through superconducting systems and reaching heavy fermion behavior. Members within a single family of compounds can provide all those very dierent ground states, and the opportunity to study and try to understand some of the electronic and magnetic fundamental interactions involved. This thesis is a result of exploring these dierent behaviors that arise from electron-electron correlations, specically in the family of cage compounds RT2Zn20 (R=Y,Gd,Yb and T=Fe,Co). A detailed combination of quantitative macroscopic and microscopic descriptions of the electronic, thermodynamic and magnetic properties of some members of this family were developed. The rst part of this thesis presents a study on Gd3+- doped YCo2Zn20 single crystals (Y1..xGdxCo2Zn20: (0.002 . x 1.00) through a combination of temperature-dependent Electron Spin Resonance (ESR), heat capacity and dc magnetic susceptibility experiments, plus collaborative rst-principles Density Functional Theory (DFT) calculations. The combination of experimental and electronic structure data establish GdCo2Zn20 as a model Ruderman-Kittel-Kasuya-Yosida (RKKY) system by predicting a Curie-Weiss temperature C = ..1:2(2) K directly from microscopic parameters, in very good agreement with the bulk value from magnetization data. The second part involves an exploration of the unconventional ferromagnetic behaviors that have been found in GdFe2Zn20, which has a relatively high ferromagnetic ordering temperature (TC = 86 K) despite being a system with wide separation between Gd3+ ions in a matrix with strong electron-electron correlation. Taking into account those correlations and itinerant molecular eld eects, analysis of our ESR results indicate that the exchange interaction between the Gd3+ is processed via the d-type of electrons at the Fermi level and becomes an exchange interaction of covalent nature (J(0)fd < 0). Our results shows that the RKKY model cannot explain the ferromagnetic behavior of this compound, and a super-exchange-like mechanism is proposed for this magnetic interaction. Increasing a little bit the level of complexity, the third part of this thesis is on the tuning of the electronic properties of the heavy fermion compound YbFe2Zn20 by chemical substitution (Cd doping). With increasing amount of Cd, the hybridization between Yb 4f electrons and the conduction electrons is weakened, which should be accompanied by a valence shift of the Yb3+ due to the negative chemical pressure eect. The combined results demonstrate excellent complementarity between positive physical pressure and negative chemical pressure, and point to a rich playground for exploring the physics of strongly correlated electron systems. Finally, this thesis ends with a general set of conclusions of the explored quantum materials.
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Mollet, Simon. "Exploration of 6-dimensional models with non trivial topology and their predictions for fermions masses and mixings, neutrino physics, flavour changing interactions and CP violation." Doctoral thesis, Universite Libre de Bruxelles, 2016. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/230863.
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In this thesis, we study several scenarios which go beyond the Standard Model of particle physics with the aim of gaining a better understanding for the multiplication of fermion families, their masses and mixings pattern and its relation to CP violation. The common feature of the models we envisaged (and the guiding principle of the thesis) is the introduction of extra space dimensions. In a first attempt to explain the fermion mass structure, we elaborate on a model with two extra-dimensions and a Nielsen- Olesen vortex background established on it. In this framework, three families in 4D can be seen as different modes of a single generation in 6D, while their extra-dimensional wavefunctions turn out highly constrained by the dynamics, which allows to determined the mass matrices with few parameters. Moreover, with a few additional hypotheses only, it is possible to simultaneously account for the striking differences between neutrinos and charged fermions. After a summary of the model, we illustrate this with the explicit formulation of a benchmark model which reproduces convincingly all the mass and mixing parameters of the Standard Model, taking advantage of new, more precise numerical solutions of the field equations, and including the recent measurements of the Standard Model scalar boson mass and of the neutrino heta_13 mixing angle (the latter has however been correctly predicted by the model before its first measurement). We then turn to the predictions which mainly concern the neutrino and gauge sectors. In the former, we remind the Majorana nature, and the natural tendency for inverted hierarchy pattern with an almost maximally suppressed neutrinoless double beta decay. On the other hand, we predict new (neutral) gauge bosons whose couplings to fermions are not flavour-diagonal but are however constrained (in their strength and their flavour structure) by the 6D anatomy of the theory. We compare their detectability in precision low energy processes and at colliders (especially at the LHC), and show that in the simplest geometries at least, the bounds from the former exclude interesting phenomenology for the latter. Nevertheless, we turn to more phenomenological effective Lagrangians with the same overall structure and in which we are able to lower the mass scale of the new bosons to a reachable energy, and thus analyse the possible signatures for LHC.In the last part of this work, we turn to the issue of CP violation and show how in certain 6D models with non simply connected topologies, it is possible to generate a non negligible CP violation at the 4D level in a pure gauge approach. We carefully study how the 4D CP symmetry is related to particular transformations of the original 6D theory and subsequently show how an incompatibility of such transformations with the compactification scheme can lead to an effective CP breaking. As a proof of concept, we build a toy model with two extra-dimensions compactified on a flat torus and end in 4D with a light neutral fermion with a non zero electric dipole moment.Dans cette thèse, nous étudions plusieurs scénarios au-delà du Modèle Standard de la physique des particules à la recherche d'une meilleure compréhension de la multiplication des familles de fermions, de leurs masses et de leurs mélanges, ainsi que la relation à laviolation de CP.La caractéristique commune à tous les modèles envisagés (et le concept sous-jacent à toute la thèse) est l'introduction de nouvelles dimensions spatiales. Dans une première tentative pour expliquer le spectre des fermions, nous développons un modèle où une structure de vortex à la Nielsen-Olesen est établie sur deux dimensions supplémentaires. Dans ce cadre, les trois familles à 4D peuvent être vues comme différents modes d'une unique génération à 6D, tandis que leur fonctions d'onde extra-dimensionnelles s'avèrent fortement contraintes par la dynamique ;ceci permet d'établir les matrices de masses en terme d'un petit nombre de paramètres. De plus, grâce à quelques hypothèses additionnelles seulement, il est possible de justifier simultanément les différences marquées entre neutrinos et fermions chargés. Nous synthétisons le modèle et l'illustrons en en formulant une réalisation particulière qui parvient à reproduire de manière convaincante tous les paramètres de masse et de mélange du Modèle Standard. Pour l'occasion, nous exploitons de nouvelles solutions aux équations des champs, numériquement plus précises, et prenons en compte les mesures récentes de la masse du boson scalaire et de l'angle de mélange heta_13 pour les neutrinos (le modèle avait cependant prédit ce dernier avant qu'il ne soit mesuré pour la première fois). Nous nous tournons ensuite vers les prédictions du modèle et qui concernent principalement le secteur des neutrinos et celui des bosons de jauge. Pour le premier, nous rappelons la nature "Majorana" des neutrinos, ainsi que la tendance naturelle à une hiérarchie inverse avec une suppression quasi maximale de la double désintégration bêta sans neutrino. D'autre part, nous prédisons de nouveaux bosons de jauge (neutres) dont les couplages aux fermions ne sont pas diagonaux dans l'espace des saveurs mais sont contraints (autant en terme de valeurs qu'en termes de structure) par l'anatomie de la théorie à 6D. Nous comparons leurs détections potentielles dans les processus de précision à basse énergie et auprès des collisionneurs (en particulier au LHC). Nous montrons que, dans les géométries les plus simples du moins, les limites imposées par les premiers excluent toute phénoménologie intéressante du côté des seconds. Toutefois, en nous tournantvers des Lagrangiens effectifs qui conservent la même structure d'ensemble mais ouvrent à une étude plus phénoménologique, nous sommes capables de réduire l'échelle de masse de ces nouveaux bosons jusqu'à une énergie accessible, et donc d'en analyser de potentielles signatures au LHC.Dans la dernière partie de ce travail, nous nous intéressons à la question de la violation de CP et montrons comment dans certains modèles à 6D avec une topologie non-simplement connexe, il est possible de générer une violation de CP non négligeable à 4D dans une approche de "pure jauge". Nous étudions attentivement comment la symétrie CP à 4D est reliée à des transformations particulières de la théorie originale à 6D, suite à quoi nous montrons comment l'incompatibilité de ces transformations avec la façon dont sont "compactifiées" les dimensions supplémentaires peut conduire à une brisure effective de CP. Pour illustrer la faisabilité de notre approche, nous élaborons un "modèle jouet" où deux dimensions supplémentaires sont compactifiées sur un tore plat, et obtenons à 4D un fermion neutre léger et qui possède un moment électrique dipolaire non nul.Doctorat en Sciences
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Snyman, Izak. "Analysis and applications of the generalised Dyson mapping." Thesis, Stellenbosch : Stellenbosch University, 2004. http://hdl.handle.net/10019.1/49829.
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Thesis (MSc)--Stellenbosch University, 2004.ENGLISH ABSTRACT: In this thesis, generalized Dyson boson-fermion mappings are considered. These are techniques used in the analysis of the quantum many-body problem, and are instances of so-called boson expansion methods. A generalized Dyson boson-fermion mapping, or a Dyson mapping for short, is a one-to-one linear but non-unitary operator that can be applied to vectors representing the states of a many-fermion system. A vector representing a fermion system maps onto a vector that is most naturally interpreted as representing a state of a many-body system that contains both bosons and fermions. The motivation for doing such a mapping is the hope that the mapping will reveal some property of the system that simplifies its analysis and that was hidden in the original form. The aims of this thesis are 1. to review the theory of generalized Dyson boson-fermion mappings, 2. by considering a tutorial example, to demonstrate that it is feasible to implement the theory and 3. to find a useful application for a generalized Dyson boson-fermion mapping, by considering a non-trivial model, namely the Richardson model for superconductivity. The realization of the first two aims mainly involve the collecting together of ideas that have already appeared in the literature, into one coherent text. Some subtle points that were treated only briefly due to space restrictions in the journal publications where the theory was first expounded, are elaborated on in the present work. On the other hand, the analysis of the Richardson Hamiltonian that uses a Dyson mapping, goes beyond what has already appeared in the literature. It is the first time that a boson expansion technique is implemented for a system where the roles of both collective and non-collective fermion pairs are important. (The Dyson mapping associates bosons with Cooper pairs, while the fermions not bound in Cooper pairs result in fermions being present in the mapped system as well.) What is found is that the Dyson mapping uncovers non-trivial properties of the system. These properties aid the construction of time-independent perturbation expansions for the stationary states of the system, as well as time-dependent expansions for transition amplitudes between states. The time-independent expansions agree with results that other authors obtained through methods other than boson expansions. The time-dependent expansions, that one would be hard-pressed to develop without a Dyson mapping, might in future prove useful in understanding aspects of the dynamics of ultracold fermi gases, when time-dependent magnetic fields are used to vary the atom-atom interaction strenght.
AFRIKAANSE OPSOMMING: In hierdie tesis word veralgemeende Dyson boson-fermion-afbeeldings ondersoek. Hierdie afbeeldings word gebruik in die analise van die kwantum veeldeeltjie probleem, en is voorbeelde van sogenaamde boson-uitbreidingstegnieke. 'n Veralgemeende Dyson bosonfermion- afbeelding, of kortweg 'n Dyson afbeelding, is 'n een-tot-een, lineêre maar nie-unitêre operator wat inwerk op vektore wat toestande verteenwoordig van 'n veel-fermion sisteem. 'n Vektor wat 'n fermionsisteem verteenwoordig word so afgebeeld op 'n vektor waarvoor die mees natuurlike interpretasie is dat dit 'n toestand verteenwoordig van 'n sisteem waarin beide bosone en fermione aanwesig is. So 'n afbeelding word gewoonlik gemaak in die hoop dat eienskappe van die sisteem, wat versteek was in die oorspronklike weergawe, voor-die-hand-liggend is na die afbeelding. Hierdie tesis het ten doel 1. om die teorie van veralgemeende Dyson boson-fermion-afbeeldings te hersien, 2. om 'n eenvoudige voorbeeld deur te werk, en so te demonstreer dat die teorie sonder moeite geïmplimenteer kan word en 3. om 'n nuttige toepassing te vind vir 'n veralgemeende Dyson boson-fermion-afbeelding deur 'n nie-triviale model, naamlik die Richardson model vir supergeleiding, te ondersoek. Die eerste twee van hierdie doelwitte behels hoofsaaklik dat idees wat reeds in die literatuur verskyn het, saamgevat word in een koherente teks. Sommige subtiele punte wat, vanwee beperkte ruimte, slegs kortliks bespreek is in die joernaalartikels waarin die teorie oorspronklik verskyn het, word in hierdie tesis meer breedvoering bespreek. Daarteenoor verteenwoordig die analise van die Richardson model met behulp van 'n Dyson afbeelding 'n nuwe bydra. Dit is naamlik die eerste keer dat 'n bosonuitbreiding ingespan word vir 'n sisteem waar sowel kollektiewe as nie-kollektiewe fermionpare 'n belangrike rol speel. (Die Dyson afbeelding assosieer bosone met die oorspronklike sisteem se Cooper pare, terwyl die fermione wat in die oorspronklike sisteem nie tot Cooper pare gebind is nie, sorg dat daar ook fermione teenwoordig is in die afgebeelde sisteem.) Ons vind dat die Dyson afbeelding nie-triviale eienskappe van die sisteem aan die lig bring. Hierdie eienskappe is nuttig vir die konstruksie van beide tyd-onafhanklike steuringsreekse vir die stasionêre toestande van die sisteem en vir tyd-afhanklike steuringsreekse vir oorgangsamplitudes tussen toestande. Die tyd-onafhanklike uitbreidings stem ooreen met resultate wat ander outeurs afgelei het sonder die gebruik van 'n Dyson afbeelding. Die tyd-afhanklike uitbreidings, wat kwalik afgelei kan word sonder 'n Dyson afbeelding, mag vorentoe nuttig wees om aspekte van die dinamika van baie koue Fermi gasse te verstaan, wanneer tydafhanklike magneetvelde gebruik word om die inter-atoomwisselwerking te manipuleer.
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Halfpap, Ole. "Quantum diffusion and scaling of localized interacting electrons." [S.l. : s.n.], 2000. http://www.sub.uni-hamburg.de/disse/317/thesis.pdf.
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Allais, Andrea. "Interacting fermions : a holographic approach/." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/83828.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2013.Cataloged from PDF version of thesis.
Includes bibliographical references (page 59).
Most materials are either metals or insulators. When they are metals, their electronic properties are usually described by Landau's Fermi liquid theory. That is, they behave more or less like a free Fermi gas, with a few modifications due to electron-electron interactions. However, there exist a few metallic materials whose phenomenology does not fit within Fermi liquid theory. These are quasi-2D metals on the verge of becoming insulators, and they happen to become superconducting at low temperature, by a mechanism different than BCS superconductivity. The physics of these materials calls for a new strongly coupled universality class of interacting electrons, yet to be understood. This work looks at the problem from the novel point of view of gauge/gravity, or holographic, duality.
by Andrea Allais.
Ph.D.
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Disertori, Margherita. "Renormalisation constructive des fermions en interaction." Palaiseau, Ecole polytechnique, 1999. http://www.theses.fr/1999EPXX0038.
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En utilisant la technique de la renormalisation constructive, nous avons developpe une technique rigoureuse pour la renormalisation des systemes fermioniques. Apres l'avoir testee sur un probleme deja bien connu (la limite ultraviolette du modele de gross-neveu massif a deux dimensions) nous l'avons etendue a la physique du solide. Dans ce contexte nous avons considere un modele simple decrivant la phase normale d'un supraconducteur en deux dimensions spatiales. En particulier nous avons donne la premiere preuve rigoureuse d'une relation, entre la constante de couplage et la temperature critique, qui a ete prevue par les theories phenomenologiques.
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Urlichs, Konrad. "Baryons and baryonic matter in four-fermion interaction models." [S.l.] : [s.n.], 2007. http://deposit.ddb.de/cgi-bin/dokserv?idn=983572755.
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Hofmann, Johannes Benedict. "Exact relations for strongly interacting fermions." Thesis, University of Cambridge, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.648470.
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ZANCHI, DRAZEN. "Fermions en faible interaction sur un reseau bidimensionnel." Paris 11, 1996. http://www.theses.fr/1996PA112284.
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Le probleme d'electrons faiblement correles, et en particulier du modele de hubbard sur un reseau carre au voisinage du demi-remplissage, est difficile a traiter a cause de la presence simultanee des divergences du type particule-particule (p-p) et particule-trou (p-t) dans l'approche perturbative. On traite ce probleme par le groupe de renormalisation a une boucle. En commencant avec l'action pour la zone de brillouin entiere (et non pas avec l'action effective de basse energie), on reduit successivement la coupure autour de la surface de fermi et on suit la renormalisation de couplage comme une fonction de trois energies-impulsions. On calcule la temperature de passage, a laquelle le flot de renormalisation passe du regime parquet, ou les canaux p-p et p-t sont egalement importants, au regime bcs, ou seulement le terme p-p joue un role. La coupure a laquelle le couplage diverge est associe a la temperature critique, etant une fonction du potentiel chimique et de l'interaction de hubbard. Afin de determiner quelles fluctuations sont critiques, on suit la renormalisation des fonctions de correlation pour l'onde de densite de spin (ods) et pour la supraconductivite (sc). Si l'instabilite se produit dans le regime parquet, les fluctuations critiques sont ods (au demi- et pres du demi-remplissage) ou bien sc (sous dopage suffisant). Si l'instabilite se produit dans le regime bcs, la seule possible est instabilite sc. Le gap sc est de la symetrie d et le parametre d'ordre ods a la symetrie s. Finalement, en calculant la copressibilite statique, on discute la possibilite de la localisation de mott-hubbard, induite par des processus umklapp. Si le flot de renormalisation devient fort deja dans le regime parquet, la copressibilite est supprime par la renormalisation de l'interaction, ce qui indique que les charges commencent a se localiser
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Chin, Jit Kee. "Strongly-interacting fermions in an optical lattice." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/45417.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2007.Includes bibliographical references (p. 131-138).
Two sets of studies are described in this thesis. The first describes studies conducted with sodium Bose-Einstein condensates (BEC) while the second focuses on the pairing of fermionic lithium-6 pairs in an optical lattice within the strongly interacting BEC-BCS regime. Common to both sets of studies is the use of a magnetically tunable Feshbach resonance to manipulate interactions between the atoms. In the first experiment, we destabilize a sodium BEC by switching its interactions from repulsive to attractive and studied the resulting dynamics. A local amplification of low momentum energetic instabilities was observed and the measured rate of amplification agreed well with theoretical predictions. For large condensates, this process depleted the condensate faster than the global inward collapse. Subsequently, I describe the major construction effort that was undertaken to convert our BEC machine to a two-species machine capable of cooling fermionic lithium-6. Upon its completion, we obtained a resonance superfluid of loosely bound 6Li pairs in the BECBCS crossover. When placed in a shallow optical lattice, long range phase coherence of this resonance superfluid was inferred from the presence of sharp interference peaks after ballistic expansion. With this observation we have obtained the first evidence of superfluidity of fermions in an optical lattice. A loss in phase coherence occurred when the lattice depth was increased past a critical value, possibly signaling a transition to an insulating state. Further preliminary explorations of this novel system is described followed by an outline of its potential for studying condensed matter phenomena like high temperature superconductivity.
by Jit Kee Chin.
Ph.D.
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Dusuel, Sébastien. "Déformation de la surface de Fermi pour un système fortement anisotrope d'électrons en interaction." Paris 7, 2002. https://tel.archives-ouvertes.fr/tel-00002124.
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Keil, Werner H. "On a 1 + 1 - dimensional interacting soliton-fermion system with supersymmetry." Thesis, University of British Columbia, 1985. http://hdl.handle.net/2429/24825.
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A supersymmetric interacting soliton-fermion system in one space and one time dimension is investigated. We construct the soliton sector of the quantum theory using a generalization of the "method of collective coordinates" previously developed for purely bosonic theories. A canonical transformation leads to a set of "collective" field variables with constraints and the transformed theory is quantized in the canonical way using Dirac's method for constrained systems. The Hamiltonian is evaluated in collective coordinates and the equations of motion are solved to first order in a perturbative expansion. We find that the field equations admit zero-energy solutions for both the boson and the fermion field.
The presence of the soliton has nontrivial consequences for the supersymmetry of the theory. The supersymmetry algebra has to be modified to include topological charges and as a result supersymmetry is spontaneously broken. It follows that the ground state is doubly degenerate. Finally, the zero-energy solutions are found to be connected with the symmetries of the theory broken by the soliton. The boson zero-mode corresponds to spatial translations, the fermion zero-mode is associated with the supersymmetryScience, Faculty of
Physics and Astronomy, Department of
Graduate
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Whitehead, Thomas Michael. "Interacting Fermi gases." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/274548.
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Interacting Fermi gases are one of the chief paradigms of condensed matter physics. They have been studied since the beginning of the development of quantum mechanics, but continue to produce surprises today. Recent experimental developments in the field of ultracold atomic gases, as well as conventional solid state materials, have produced new and exotic forms of Fermi gases, the theoretical understanding of which is still in its infancy. This Thesis aims to provide updated tools and additional insights into some of these systems, through the application of both numerical and analytical techniques. The first Part of this Thesis is concerned with the development of improved numerical tools for the study of interacting Fermi gases. These tools take the form of accurate model potentials for the dipolar and contact interactions, as found in various ultracold atomic gas experiments, and a new form of Jastrow correlation factor that interpolates between the radial symmetry of the inter-electron Coulomb potential at short inter-particle distances, and the symmetry of the numerical simulation cell at large separation. These methods are designed primarily for use in quantum Monte Carlo numerical calculations, and provide high accuracy along with considerable acceleration of simulations. The second Part shifts focus to an analytical analysis of spin-imbalanced Fermi gases with an attractive contact interaction. The spin-imbalanced Fermi gas is shown to be unstable to the formation of multi-particle instabilities, generalisations of a Cooper pair containing more than two fermions, and then a theory of superconductivity is built from these instabilities. This multi-particle superconductivity is shown to be energetically favourable over conventional superconducting phases in spin-imbalanced Fermi gases, and its unusual experimental consequences are discussed.
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Naïdja, Houda. "Etude microscopique de systèmes fermioniques finis : corrélations dans les noyaux atomiques et gaz d'électrons confinés par un potentiel harmonique en présence d'un champ magnétique." Thesis, Bordeaux 1, 2009. http://www.theses.fr/2009BOR13762/document.
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Dans le cadre d'une approche Higher Tamm Dancoff Approximation notée HTDA, nous avons étudié les corrélations vibrationnelles de type quadrupole, avec et sans appariement. Le champ moyen a été déterminé dans le cadre d'une approche microscopique utilisant l'interaction effective de Skyrme. Une interaction résiduelle schématique de type delta plus quadrupole-quadrupole, tenant compte en particulier de l'appariement neutron-proton T=0 et T=1 a été utilisé. Les résultats obtenus pour la résonance géante quadrupolaire isoscalaire du noyau Ca40 ont été comparés aux données expérimentales et à d'autres résultats théoriques. Nous avons également étudié un gaz de fermions piégés dans un potentiel d'oscillateur harmonique à 2D, et à température nulle, en présence d'un champ magnétique uniforme. Les expressions exactes des quelques grandeurs thermodynamiques ont été dérivées à partir de la matrice densité de BlochWithin the framework of the so-called Higher Tamm Dancoff Approxiamtion (HTDA), we have studied the quadrupole vibrational correlations with and without pairing correlations. The mean field has been determined within a microscopic approach using the Skyrme effective interaction. A schematic residual interaction of the delta plus quadrupole-quadrupole type, allowing in particular neutron-proton T=0 and T=1 pairing, has been used. The results which have been obtained for the isoscalar quadrupole giant resonance of the Ca40 have been compared with the experimental data. A fermion gaz trapped in a 2D harmonic oscillator well at zero temperature and in the presence of a uniform magnetic field has been investigated. Exact expressions of some thermodynamic quantities have been derived from the Bloch density matrix
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Dos, Santos Luiz Henrique Bravo. "Topological Properties of Interacting Fermionic Systems." Thesis, Harvard University, 2012. http://dissertations.umi.com/gsas.harvard:10195.
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This thesis is a study of three categories of problems in fermionic systems for which topology plays an important role: (i) The properties of zero modes arising in systems of fermions interacting with a bosonic background, with a special focus on Majorana modes arising in the superconductor state. We propose a method for counting Majorana modes and we study a mechanism for controlling their number parity in lattice systems, two questions that are of relevance to the protection of quantum bits. (ii) The study of dispersionless bands in two dimensions as a platform for correlated physics, where it is shown the possibility of stabilizing the fractional quantum Hall effect in a flat band with Chern number. (iii) The extension of the hierarchy of quantum Hall fluids to the case of time-reversal symmetric incompressible ground states describing a phase of strongly interacting topological insulators in two dimensions.Physics
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Feld, Michael. "Low temperature phases of interacting fermions in two dimensions." Thesis, University of Cambridge, 2011. https://www.repository.cam.ac.uk/handle/1810/252257.
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Motruk, Johannes. "Characterization of topological phases in models of interacting fermions." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-206990.
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The concept of topology in condensed matter physics has led to the discovery of rich and exotic physics in recent years. Especially when strong correlations are included, phenomenons such as fractionalization and anyonic particle statistics can arise. In this thesis, we study several systems hosting topological phases of interacting fermions.
In the first part, we consider one-dimensional systems of parafermions, which are generalizations of Majorana fermions, in the presence of a Z_N charge symmetry. We classify the symmetry-protected topological (SPT) phases that can occur in these systems using the projective representations of the symmetries and find a finite number of distinct phases depending on the prime factorization of N. The different phases exhibit characteristic degeneracies in their entanglement spectrum (ES). Apart from these SPT phases, we report the occurrence of parafermion condensate phases for certain values of N. When including an additional Z_N symmetry, we find a non-Abelian group structure under the addition of phases.
In the second part of the thesis, we focus on two-dimensional lattice models of spinless fermions. First, we demonstrate the detection of a fractional Chern insulator (FCI) phase in the Haldane honeycomb model on an infinite cylinder by means of the density-matrix renormalization group (DMRG). We report the calculation of several quantities characterizing the topological order of the state, i.e., (i)~the Hall conductivity, (ii)~the spectral flow and level counting in the ES, (iii)~the topological entanglement entropy, and (iv)~the charge and topological spin of the quasiparticles. Since we have access to sufficiently large system sizes without band projection with DMRG, we are in addition able to investigate the transition from a metal to the FCI at small interactions which we find to be of first order.
In a further study, we consider a time-reversal symmetric model on the honeycomb lattice where a Chern insulator (CI) induced by next-nearest neighbor interactions has been predicted by mean field theory. However, various subsequent studies challenged this picture and it was still unclear whether the CI would survive quantum fluctuations. We therefore map out the phase diagram of the model as a function of the interactions on an infinite cylinder with DMRG and find evidence for the absence of the CI phase. However, we report the detection of two novel charge-ordered phases and corroborate the existence of the remaining phases that had been predicted in mean field theory. Furthermore, we characterize the transitions between the various phases by studying the behavior of correlation length and entanglement entropy at the phase boundaries. Finally, we develop an improvement to the DMRG algorithm for fermionic lattice models on cylinders. By using a real space representation in the direction along the cylinder and a real space representation in the perpendicular direction, we are able to use the momentum around the cylinder as conserved quantity to reduce computational costs. We benchmark the method by studying the interacting Hofstadter model and report a considerable speedup in computation time and a severely reduced memory usage.
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Lee, Ye-Ryoung. "Ultracold Fermi gas with repulsive interactions." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/79520.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2012.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 95-100).
This thesis presents results from experiments of ultracold atomic Fermi gases with repulsive interaction. Itinerant ferromagnetism was studied by simulating the Stoner model with a strongly interacting Fermi gas of ultracold atoms. We observed nonmonotonic behavior of lifetime, kinetic energy, and size for increasing repulsive interactions, which is in good agreement with a mean-field model for the ferromagnetic phase transition. However, later research showed the absence of enhanced spin fluctuation, which is definitive evidence against the ferromagnetic phase transition. Still, our work triggered a lot of research on repulsive interactions in ultracold Fermi gases. A quantitative approach is taken to study ultracold Fermi gases with repulsive interaction. This is done by careful measurements of density profiles in equilibrium. First, Pauli paramagnetism is observed in trapped atomic samples which have an inhomogeneous density due to the harmonic confinement potential. We experimentally measure the susceptibility of ideal Fermi gas. This research shows that ultracold atoms can serve as model systems to demonstrate well-known textbook physics in a more ideal way than other systems. Then, Fermi gases with repulsive interactions are characterized by measuring their compressibility as a function of interaction strength. The compressibility is obtained from in-trap density distributions monitored by phase contrast imaging. For interaction parameters kFa > 0.25 fast decay of the gas prevents the observation of equilibrium profiles. For smaller interaction parameters, the results are adequately described by first-order perturbation theory. A novel phase contrast imaging method compensates for dispersive distortions of the images.
by Ye-Ryoung Lee.
Ph.D.
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Bruce, A. M. "Studies of the interacting Boson-Fermion model in the W-Os-Pt nuclei." Thesis, University of Manchester, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.375080.
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Dusuel, Sebastien. "Déformation de la surface de Fermi pour un système fortement anisotrope d'électrons en interaction." Phd thesis, Université Paris-Diderot - Paris VII, 2002. http://tel.archives-ouvertes.fr/tel-00002124.
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Nous étudions certains aspects de la physique des fermions en deux dimensions, pertinente pour les conducteurs organiques quasi unidimensionnels et les supraconducteurs à haute température critique. En particulier, nous nous intéressons au calcul de la surface de Fermi de systèmes électroniques en interaction, qui est une des informations cruciales du point de vue des propriétés de basse énergie de ces systèmes. Nous commençons par donner une interprétation énergétique, sur un toy model, de la déformation de la surface de Fermi due aux interactions entre électrons, en insistant sur la nécessité d'une méthode auto-cohérente. Puis nous expliquons comment faire le même calcul dans un cadre de théorie des champs, et comment améliorer les résultats grâce à un groupe de renormalisation. Nous appliquons ce formalisme aux composés quasi unidimensionnels. Un des chapitres est un résumé d'un article dans lequel nous analysons la pertinence d'une transition d'un état onde de densité de spin à un état supraconducteur, observée dans les flots de renormalisation d'un modèle de fermions à deux dimensions, dont la surface de Fermi est un carré avec des coins arrondis.
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Potter, Charles D. "Search for evidence of fermi surface nesting in Bi₂Sr₂Ca₁Cu₂O₈." Diss., Virginia Tech, 1992. http://hdl.handle.net/10919/40088.
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Levinsen, Jesper F. "Paired fermionic superfluids with s- and p-wave interactions." Connect to online resource, 2007. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3284444.
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Jäckel, Jörg. "Effective actions for strongly interacting fermionic systems." [S.l. : s.n.], 2003. http://deposit.ddb.de/cgi-bin/dokserv?idn=968788351.
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Schmidt, Ludwig. "Etude sous pression du fermion lourd URu2Si2." Grenoble 1, 1993. http://www.theses.fr/1993GRE10197.
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L'objet de cette these est l'etude de la resistivite du fermion lourd uru#2si#2 dans la gamme de temperature: 35 mk (limite donnee par notre cryostat a dilution) et la temperature ambiante. Nous avons utilise deux parametres exterieurs plus ou moins reversibles: un champ magnetique variant entre 0 et 12t, et une pression hydrostatique, variant entre 0 et 70 kbar. Ces parametres servent a creer des conditions dans lesquelles chacun des mecanismes responsables de la resistivite repond d'une facon differente aux mesures de transport que sans champ et pression. Dans la partie experimentale l'adaptation d'un cryostat a dilution au probleme est decrite, avec les bobines et les cellules de pression, et l'ensemble des echantillons mesures est presente. Nos mesures de resistivite, la modelisation de la resistivite et de la chaleur specifique dans les phases antiferromagnetique et normale sont donnees dans le troisieme chapitre. L'analyse se concentre essentiellement sur la phase antiferromagnetique: nous montrons que la formation d'ondes de spin dues aux interactions entre les electrons f localises et les electrons de conduction domine les proprietes thermodynamiques et de transport. Nous abordons la supraconductivite de uru#2si#2 sous champ magnetique et sous pression et presentons nos mesures du deuxieme champ critique. Une comprehension de cette phase est rendue difficile par des problemes d'origine intrinseque (courbure positive pres de t#c, forme et anisotropie du champ critique) et extrinseques (largeur des transitions supraconductrices)
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Pantel, Pierre-Alexandre. "Étude théorique d’un gaz de fermions froids en interaction : aspects dynamiques et effets de polarisation." Thesis, Lyon 1, 2014. http://www.theses.fr/2014LYO10167/document.
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Les progrès techniques réalisés dans le cadre des expériences sur les gaz de fermions ultrafroids ont engendré une émulation particulièrement importante ces dernières années. En effet, ces dispositifs expérimentaux permettent de produire des systèmes gazeux ≪ à la carte ≫, notamment grâce au phénomène de résonances de Feshbach qui permet de contrôler le signe de la longueur de diffusion a par application d'un champ magnétique extérieur. Il est alors possible de générer aussi bien une interaction attractive (a < 0) que répulsive (a > 0). La résonance de Feshbach en elle-même se trouve en a → ±∞, cette limite correspondant à un régime de fortes corrélations entre les particules. De plus, dans la région où a est positive, des états lies moléculaires (bosoniques car formés de deux fermions) peuvent se former. En-dessous d'une certaine température, une phase superfluide peut alors apparaitre, et une transition de phase continue entre l'état bosonique et l'état fermionique peut être observée (BEC-BCS crossover). En fonction de la position dans le diagramme de phases, les modes collectifs possèderont des caractéristiques (fréquence, amortissement) différentes. En ce sens, ils constituent une sonde de l'état de la matière et une connaissance précise de ces modes est par conséquent très importante. Le travail présenté dans cette thèse comporte une caractérisation détaillée de plusieurs modes collectifs dans la phase normale du système atomique. L'étude repose principalement sur l'équation de Boltzmann, que nous résolvons de deux façons différentes. La première consiste à utiliser une méthode des moments ≪ améliorée ≫ (c'est-à-dire d'ordre supérieur). La seconde est numérique et a nécessité l'écriture d'un programme de simulation permettant l'incorporation de tous les effets de milieu (potentiel de champ moyen et section efficace). Une attention toute particulière a été apportée à la mise en place des simulations afin de reproduire le plus fidèlement possible les conditions expérimentales. Les techniques expérimentales permettent également désormais la création de gaz polarisés. Nous présenterons donc dans ce travail une étude de ces gaz utilisant notre programme de simulation (mise en évidence des différents régimes de collision), puis une étude plus théorique ayant pour principal objectif d'établir le diagramme de phase encore méconnu de ces gaz particuliers, et enfin de proposer une méthode de calcul des effets de milieu, les techniques habituelles utilisées pour les gaz non polarisés n'étant plus valablesTechnical progress on ultra-cold Fermi gases experiments induced numerous studies for the last few years. Using these experimental setups, it is effectively possible to generate ultra-cold gases with selected properties, in particular through the Feshbach resonances phenomenon. This allows us to set the sign of the scattering length a using an external magnetic field. It is then possible to have an attractive interaction (a < 0) as well as a repulsive one (a > 0). The Feshbach resonance itself is defined for infinite values of a (positive or negative), which corresponds to a strongly interacting regime. Moreover, when a > 0, molecular bound states (bosonic because they are made with two fermionic atoms) can appear. Thus, below a critical temperature, a superfluid phase can emerge and a crossover can be observed (from the BEC to BCS superfluid states). Depending on the position on the phase diagram, frequency and damping of collective modes will be different. This is why the collective modes are good probes of the system phase. A precise extensive knowledge of their characteristics is thus very important. This thesis presents a complete study of some of these collective modes in the normal phase. This work mainly relies on the Boltzmann equation which will be solved in two different ways: firstly, with an improved (higher order) version of the so-called moments method; secondly with a numerical solution that has required to write a numerical code in order to take into account the in-medium effects (mean field potential and in-medium cross section). Particular attention has been paid to numerical simulations in order to reproduce as closely as possible the experimental conditions. Moreover, experimental procedures now allow to create spin unbalanced gases. We have shown in this work a study of these systems using the numerical resolution of the Boltzmann equation. Moreover, we have developed a theoretical approach in order to build the phase diagram of these polarized gases, which is not fully described yet. Finally, we have suggested a method to determine the in-medium effects, with the aim to solve the problem emerging with the usual method used in the balanced case
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Radhi, Fahmi Sha'ban. "Studies of 76Se and 75As by gamma-ray spectroscopy and interacting Boson (-Fermion) models." Thesis, Royal Holloway, University of London, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.338872.
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Goff, Leonard Thomas. "Surface codes, the 2D classical Ising model, and non-interacting fermions." Thesis, University of British Columbia, 2011. http://hdl.handle.net/2429/36374.
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In this thesis, we consider the task of simulating measurement-based quantum computation (MBQC) on surface code states: the generalization of Kitaev's toric code to graphs embedded on a surface of higher genus. We define a family of higher genus graphs and a simple ordering of single qubit measurements, and find that simulating MBQC on any of the associated surface code states is equivalent to evaluating the inner-product between a product state and a surface code state on another graph. We further find that such an inner-product can always be written as a sum of one or more 2D classical Ising model partition functions, with appropriate couplings. For certain higher genus square lattices, we develop a means to evaluate this partition function in a number of steps that scales polynomially in the number of qubits, but exponentially in the genus of the embedded graph. The method makes use of the transfer matrix formalism for the Ising partition function, and a subsequent mapping to fermion operators. We synthesize these results to relate the simulation of MBQC on certain surface code states to a system of fermions interacting with the encoded qubits of the surface code. We identify a family of states in the code space of the surface code on our higher genus graphs for which MBQC can be simulated efficiently in all parameters, including the genus of the embedded graph. Finally, we identify two connections between the complexity of this task and entanglement.
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de, Coster George. "Effective Soft-Mode Theory of Strongly Interacting Fermions in Dirac Semimetals." Thesis, University of Oregon, 2019. http://hdl.handle.net/1794/24235.
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We present an effective field theory for interacting electrons in clean semimetals (both three dimensional Dirac semimetals and graphene) in terms of their soft or massless bosonic degrees of freedom. We show, by means of a Ward identity, that the intrinsic semimetal ground state breaks the Sp(4M) symmetry of the theory. In Fermi liquids this enables one to identify the massive, non-Goldstone modes of the theory and integrate them out. Due to the vanishing density of states in semimetals, unlike in Fermi liquids, both Goldstone and non-Goldstone modes are equally soft, and so all two-particle correlations need to be kept. The resulting theory is not perturbative with respect to the electron-electron interaction; rather, it is controlled by means of a systematic loop expansion and allows one to determine the exact asymptotic form of observables in the limits of small frequencies and/or wave vectors. Equivalently, it provides a mechanism of determining the long time-tail and long wavelength behavior of observables and excitations. As a representative application, we use the theory to compute the zero-bias anomaly for the density of states for both short and long-range interactions in two and three dimensions. We find that the leading nonanalyticity in semimetals with a long-ranged interaction appears at the same order in frequency as the one in Fermi liquids, since the effects of the vanishing density of states at the Fermi level are offset by the breakdown of screening. Consequently, we are able to provide a logical scheme to determine the leading non-analytical behavior of observables in semimetals using knowledge of the corresponding non-analyticities in a Fermi liquid.2020-01-11
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Günter, Kenneth John. "Interacting Fermi gases and Bose-Fermi mixtures in optical lattices." Zürich : ETH, 2007. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=17446.
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VAN, DEN BOSSCHE MATHIAS. "Fermions a une dimension : etude du modele a interaction par sauts de paires." Paris 6, 1996. http://www.theses.fr/1996PA066718.
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Nous etudions le modele a interaction par sauts de paires unidimensionnel a temperature nulle. Il existe une controverse quant a la nature de son etat fondamental. En effet, deux etudes numeriques a petites tailles indiquent que le modele presente une transition de phase dans l'etat fondamental pour une valeur finie du couplage. Inversement, le groupe de renormalisation perturbatif exclut une telle transition. Nous presentons une serie de resultats obtenus d'abord par diagonalisation exacte du hamiltonien, puis groupe de renormalisation numerique par la matrice densite. En interpretant ces resultats dans le cadre de la theorie des liquides de luttinger nous proposons un scenario qui permet de rendre compte de tous les resultats obtenus sur ce modele. A basses energies, le modele est donc equivalent au modele de hubbard attractif, et ne presente pas de transition de phase.
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PASCAUD, MICHAEL. "Magnetisme orbital de conducteurs mesoscopiques desordonnes et proprietes spectrales de fermions en interaction." Paris 11, 1998. http://www.theses.fr/1998PA112319.
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La coherence de phase des fonctions d'onde electroniques engendre une contribution au magnetisme orbital d'un conducteur, qui generalise la notion de courant permanent pour un anneau. Dans un conducteur desordonne diffusif, la moyenne sur le desordre de l'aimantation, ou ses fluctuations, peuvent s'exprimer en fonction de la probabilite classique de retour a l'origine. Apres avoir generalise le calcul de la probabilite de retour pour des conducteurs quasi-unidimensionnels multiplement connexes, nous avons calcule la moyenne ou les fluctuations de l'aimantation (par anneau) pour differents reseaux d'anneaux connectes : elles restent finies dans la limite d'un grand nombre d'anneaux (et du meme ordre que pour un anneau isole). Un developpement perturbatif, base sur une image physique simple, permet de retrouver aisement ces resultats. Enfin dans le cas d'une geometrie quasi-unidimensionnelle plus complexe, nous avons etudie la distribution spatiale de la moyenne de la densite du courant permanent et de ses fluctuations. La deuxieme partie de la these concerne les proprietes statistiques des etats propres d'un liquide de fermi desordonne en interaction. En utilisant la structure hierarchique de l'espace de fock de ce probleme, nous avons retrouve, sous certaines conditions, le critere de la transition entre un regime de basse energie (ou les etats propres sont completement decorreles) et un regime de haute energie (ou leurs correlations sont semblables a celles de wigner-dyson).
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Fräßdorf, Christian [Verfasser]. "Field Theories of Interacting and Disordered Dirac Fermions in Graphene / Christian Fräßdorf." Berlin : Freie Universität Berlin, 2019. http://d-nb.info/1183675682/34.
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Moosavi, Per. "Interacting fermions and non-equilibrium properties of one-dimensional many-body systems." Licentiate thesis, KTH, Teoretisk fysik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-193330.
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Recent experimental progress on ultracold atomic gases have opened up the possibility to simulate many-body systems out of equilibrium. We consider such a system described by the Luttinger model, which is a model of interacting fermions in one spatial dimension. It is well known that the Luttinger model is exactly solvable using bosonization. This also remains true for certain extensions of the model, e.g., where, in addition, the fermions are coupled to phonons. We give a self-contained account of bosonization, together with complete proofs, and show how this can be used to solve the Luttinger model and the above fermion-phonon model rigorously. The main focus is on non-equilibrium properties of the Luttinger model. We use the exact solution of the Luttinger model, with non-local interactions, to study the evolution starting from a non-uniform initial state with a position-dependent chemical potential. The system is shown to reach a current-carrying final steady state, in which the universal value of the electrical conductance, known from near-to-equilibrium settings, is recovered. We also study the effects of suddenly changing the interactions and show that the final state has memory of the initial state, which is, e.g., manifested by non- equilibrium exponents in its fermion two-point correlation functions.QC 20161003
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Kim, YÅ ng-baek. "Interaction of composite fermions with a gauge field in the fractional quantum Hall regime." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/32672.
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Fröhlich, Bernd. "A strongly interacting two-dimensional Fermi gas." Thesis, University of Cambridge, 2011. https://www.repository.cam.ac.uk/handle/1810/252252.
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Ku, Mark. "Strongly-interacting Fermi gases with population imbalance." Thesis, University of British Columbia, 2009. http://hdl.handle.net/2429/12629.
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This thesis presents a theoretical study of strongly-interacting Fermi systems with population imbalance, which is motivated by some differences in cold atoms experiments. We calculate the energy of a single fermion interacting resonantly with a Fermi sea of different species fermions in anisotropic traps, and show that finite particle numbers and the trap geometry impact the phase structure and the critical polarization, the limit of resonance superfluidity in traps. Our findings contribute to understanding some experimental discrepancies as finite-size and confinement effects. For an imbalanced gas in the uniform system, we calculate the energy of adding an impurity, and construct the equation of state of the partially-polarized normal Fermi liquid. Finally, we study the properties of a spin-down polaron in a trapped gas containing arbitrary numbers of spin-up and spin-down fermions, and derive a self-consistent equation for the polaron energy.
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Baldwin, James. "Two level systems interacting with Fermi liquids." Thesis, University of Birmingham, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.555318.
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Stan, Claudiu Andrei. "Experiments with interacting Bose and Fermi gases." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/34384.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2005.Includes bibliographical references (p. 191-204).
In the past few years, the study of trapped fermionic atoms evolved from the first cooling experiments which produced quantum degenerate samples to becoming one of the most exciting branches of current atomic physics research. This thesis covers experiments done throughout this period, which can be grouped in three sets of studies. First, degenerate 6Li Fermi gases have been produced by sympathetic cooling with bosonic 23Na. For this, an existing 23Na Bose-Einstein condensation apparatus was upgraded to an experiment capable of producing degenerate 6Li Fermi gases and 6Li-23Na degenerate Fermi-Bose mixtures. The cooling methods have been developed in two different stages, resulting in the production of degenerate 6Li Fermi gases with temperatures below 0.05 TF and up to 7 x 107 atoms, and of degenerate 6Li-23Na mixtures with a few million atoms in each of the components. Second, the properties of 6Li-23Na mixtures at different magnetic fields have been investigated, resulting in the discovery of three interspecies 6Li-23Na Feshbach resonances, which opens up the possibility to study strongly interacting Bose-Fermi mixtures in this system. This investigations also led to the observation of other Feshbach resonances in 6Li and 23Na. Third, the properties of strongly interacting 6Li spin mixtures in the strong interacting regime near a Feshbach resonance have been investigated. Weakly bound 6Li2 molecules have been produced and Bose condensed on the repulsive side of the Feshbach resonance. Pure molecular condensates with up to 3 x 106 molecules have been produced.
(cont.) The properties of the interacting Fermi gas were investigated on the attractive side of the resonance using rapid field ramps to the other side of the resonance. Fermion pairing, and condensation of these pairs was observed near the resonance, offering evidence for superfluid behavior in a strongly interacting Fermi gas.
by Claudiu Andrei Stan.
Ph.D.
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D'Elia, Claudio. "A two-body study of dynamical expansion in the XXZ spin chain and equivalent interacting fermion models." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2014. http://amslaurea.unibo.it/7604/.
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Lo scopo di questa tesi è studiare l'espansione dinamica di due fermioni interagenti in una catena unidimensionale cercando di definire il ruolo degli stati legati durante l'evoluzione temporale del sistema.
Lo studio di questo modello viene effettuato a livello analitico tramite la tecnica del Bethe ansatz, che ci fornisce autovalori ed autovettori dell'hamiltoniana,
e se ne valutano le proprietà statiche. Particolare attenzione è stata dedicata alle caratteristiche dello spettro al variare dell'interazione tra le due particelle
e alle caratteristiche degli autostati. Dalla risoluzione dell'equazione di Bethe vengono ricercate le soluzioni che danno luogo a stati legati delle due particelle e se ne valuta lo spettro energetico in funzione del momento del
centro di massa. Si è studiato inoltre l'andamento del numero delle soluzioni, in particolare delle soluzioni che danno luogo ad uno stato legato, al variare della lunghezza della catena e del parametro di interazione.
La valutazione delle proprietà dinamiche del modello è stata effettuata tramite l'utilizzo dell'algoritmo t-DMRG (time dependent - Density Matrix Renormalization Group). Questo metodo numerico, che si basa sulla decimazione
dello spazio di Hilbert, ci permette di avere accesso a quantità che caratterizzano la dinamica quali la densità e la velocità di espansione. Da queste sono stati estratti i proli dinamici della densità e della velocità di espansione al variare del valore del parametro di interazione.
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Forsythe, D. "The evolution of Fermi liquid interactions in Sr2RuO4 under pressure." Thesis, University of Cambridge, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.599130.
Full textAbstract:
There is strong evidence that a common pairing mechanism is in operation in many classes of unconventional superconductor that is related to the proximity of a magnetic quantum critical point. Hydrostatic pressure has been shown to be an effective means to tune systems near to quantum critical regions and some of the most convincing evidence linking superconductivity to magnetism has emerged from such experiments. In this work, we describe the development of a unique system that couples this high pressure tuning technique with the powerful normal state probe of quantum oscillations, in order to test models of superconductivity that make quantitative predictions regarding the normal state. As a first application, we examine how the quantum oscillation spectrum of the exotic superconductor Sr2RuO4 evolves up to pressures in excess of 30 kbar and through a region in the phase diagram previously thought to contain a quantum critical point. Combining these experiments with conventional low field measurements of the T2 A-coefficient of the resistivity and the upper critical field, we discuss the implications of our new results to possible pressure phase diagrams in the context of the "Magnetic Interaction Model", and adaptation of BCS theory to magnetic interactions. As an extension, by analysing interference effects in the oscillation spectra, we have been able to extract extremely accurate values for cylindrically symmetric contributions to the c-axis dispersion in Sr2RuO4. Access to the total warping is restricted for the α and β sheets, but we find a striking reduction under pressure in the warping of the γ sheet, which is thought to be the active band in orbital dependent theories of superconductivity. In such a scenario, this indicates a reduction in the coupling between the active and passive bands. More generally, it implies a reduced effective dimensionality in the γ sheet, which might act to suppress superconductivity via fluctuation effects.
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Costa, Louis. "An interacting Fermi-Fermi mixture at the crossover of a narrow Feshbach resonance." Diss., lmu, 2011. http://nbn-resolving.de/urn:nbn:de:bvb:19-131291.
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Kleeberg, Katja [Verfasser]. "Dyson-Schwinger Equations for strongly interacting fermions on the hexagonal graphene lattice / Katja Kleeberg." Gießen : Universitätsbibliothek, 2019. http://d-nb.info/1200352521/34.
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Lang, Gladys Hau-Wan Goddard William A. Koonin Steven E. "Auxiliary-field Monte Carlo methods for interacting fermions application to the nuclear shell model /." Diss., Pasadena, Calif. : California Institute of Technology, 1993. http://resolver.caltech.edu/CaltechTHESIS:10222009-160215418.
Full textAbstract:
Thesis (Ph. D.)--California Institute of Technology, 1993. UM #93-25,365.Advisor names found in the Acknowledgments pages of the thesis. Title from home page. Viewed 01/22/2010. Includes bibliographical references.