Thèse de doctorat : Université de Fribourg, 2008.
Despite its apparent simplicity and even if it has been studied intensively in various contexts, the two-dimensional Hubbard model is not yet completely understood. In particular when it describes a system with an intermediate interaction, out of range for perturbative methods, its ground state is still not well known. The discovery in 1986 of a superconducting phase in the copper oxides...
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Thèse de doctorat : Université de Fribourg, 2002 ; no 1367.
The Mott metal-insulator transition is investigated as a quantum phase transition. The U - t - t’ model at half-filling is considered as a paradigm; the sign of t’ is not relevant and is taken to be positive. The phase diagram presents two Mott insulating phases with distinct symmetries and one global metallic phase which is presumed to be a Luttinger liquid for the charge degrees of freedom....
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Thèse de doctorat : Université de Fribourg : 2002 ; 1374.
Interacting e1ectrons in two dimensions are of particular interest in relation to high-temperature superconductivity. In this thesis, I study a two-dimensional extended Hubbard model in the weak coupling limit. Quite generally, the electron gas is unstable towards a superconducting state even in the absence of phonons. However in the special case of a half-filled band, the Fermi surface is nested...
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