Estado fundamental do modelo de Hubbard estendido na cadeia AB2

AUTOR(ES)

David Rafael de Barros Silva

DATA DE PUBLICAÇÃO

2008

RESUMO

In this dissertation we study the extended Hubbard model in the AB2 chain. The model hamiltonian contains a kinetic term, parameterized by t, and two terms of coulomb repulsion,U (intra-site) and V (inter-site). Considering a peculiar local exchange symmetry of the chain, as well as global symmetries of the Hubbard hamiltonian, we have applied the numerical method of density matrix renormalization group with open boundary conditions, focusing our efforts on determining the fundamental state of the system. We obtained the phase diagram produced by the competition between U and V at half filling, one electron per site. We compare our results, obtained for a system of twenty-four cells, with those obtained by the method of exact diagonalization for a system with six cells. We identified three relevant regions: for V .U/4 we find a ferrimagnetic state, which is a continuation of the phase found at V = 0, which fits in the well known Liebâs theorem; for V &U/4, were characterized regions of phase separation with the coexistence of insulator (and paramagnetic) and metal (and ferromagnetic) regions, and a phase reminiscent of that found for U = 0. The characterization of the regions was carried out by the measure of the charge and spin profiles, as well as with the study of the energy as a function of the model parameters

ASSUNTO(S)

extended hubbard model fisica grupo de renormalizaÃÃo da matriz densidade modelo de hubbard estendido ferrimagnetismo phase separation ferrimagnetism ferromagnetism density matrix renormalization group ferromagnetismo separaÃÃo de fases

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