Suscetibilidades de carga e spin para uma superfície de fermi chata bidimensional

AUTOR(ES)
DATA DE PUBLICAÇÃO

2006

RESUMO

In this work we investigate the charge and spin instabilities of a two-dimensional model (d=2) of strongly interacting electrons in the presence of a at Fermi surface (FS) by using the renormalization group theory (RG). Bearing in mind the strong electronic repulsions in the cuprates superconductors, we try to relate our model to the repulsive Hubbard model in d = 2 as much as possible. By means of perturbation theory we calculate the Green functions of the physical system. After that, we apply the RG concept to regularize all the logarithm divergences generated by the microscopic model in the perturbation theory. To test the accuracy of our approach, we employ our techniche for the one-dimensional case exploring the spin symmetries to dene the susceptibilities of the charge density wave (CDW) type, of the spin density wave (SDW) type, of the singlet superconductivity (SSC) type and, nally, of the triplet superconductivity (TCS) type that play an important role for the construction of the phase diagram in coupling space. In our two-loop approach, it becomes clearer the validity of the Mermin and Wagner theorem for both cases d = 1; 2. In our two-dimensional case, we see that, following what happens in d = 1, there are no stable quasiparticles in the physical system for strong coupling repulsive regime. This, as we know, invalidates Landau Fermi liquid representation. We show also that, for the two-dimensional case, there exists an additional intrinsic symmetry of our model to be explored if we take into account the variation of the response functions with respect the change of sign of the momentum along the FS. In this way, we dene others susceptibilities that play an important role in the problem of the cuprates superconductors like the charge density waves of types s and d (CDW), the spin density waves of types s and d (SDW), the singlet superconductivities of types s and d (SSC) and, nally, the triplet superconductivities of types s and d (TSC). Finally, we construct the phase diagram in coupling space in our two-loop approach displaying all the dominant susceptibilities for all regimes of interaction. In the repulsive regime, which is our case of interest, the SDW+ susceptibility appear in a pronounced manner. Despite that the divergence of the SDW+ susceptibility is an artifact of the approximation and only signals that the reinforcement of the antiferromagnetic uctuations in the system. In contrast, at the same regime, all others susceptibilities ow to xed values and as a result are not being reinforced in the physical system. We conclude this work calling attention to the open problems int his eld and to the importance in establishing the FS topology to elucidate the origin of the anisotropic pseudogap in the cuprates superconductors.

ASSUNTO(S)

suscetibilidade (física) fisica supercondutividade

ACESSO AO ARTIGO

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