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Le modèle de Hubbard SU(4) à une dimension : une approche de la dégénérescence orbitale

Abstract : This thesis is dedicated to the study of orbital degeneracy in one-dimensional strongly correlated electron systems. A simple model is defined which maximally accounts for orbital degeneracy: the SU(4)-symmetric Hubbard model. The zero temperature phase diagram is obtained using analytical methods (bosonization, conformal field theory, renormalization group). Our theoretical predictions are compared to quantum Monte Carlo simulations. In the critical phases, the conformal field theory describing the universality class of the model is identified. In the massive phases, we derive the low energy effective theory, which turns out to be quasi-integrable. This allows for a description of the low lying collective modes. The phase diagram of the model is surprisingly rich, in spite of its simplicity. An interesting feature is the existence of a Mott insulator with no magnetic order at half filling. In the second part of the thesis, realistic physical processes which break the SU(4) symmetry are taken into account. The stability of the phases of the SU(4) Hubbard model under these perturbations is studied. The generic tendency is the appearance of a gaped spin liquid. Exact (non perturbative) discrete symmetries of the phase diagram are revealed. These symmetries connect different spin liquids and allow for a classification of the gaped spin liquid phases for a two-leg spin ladder in the vicinity of the SU(4) symmetric line. Two broad classes of gaped spin liquids are found, one associated with diagonal (charge density wave-like) order, the other supporting a superconducting instability.
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Contributor : Edouard Boulat <>
Submitted on : Saturday, June 12, 2004 - 2:09:24 AM
Last modification on : Wednesday, December 9, 2020 - 3:11:56 PM
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  • HAL Id : tel-00006256, version 1


Edouard Boulat. Le modèle de Hubbard SU(4) à une dimension : une approche de la dégénérescence orbitale. Matière Condensée [cond-mat]. Université Pierre et Marie Curie - Paris VI, 2003. Français. ⟨tel-00006256⟩



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