Pseudogap e energia cinética de supercondutores não convencionais descritos por um modelo de Hubbard em duas dimensões

Detalhes bibliográficos
Ano de defesa: 2020
Autor(a) principal: Motta, Giordano Paulo da
Orientador(a): Não Informado pela instituição
Banca de defesa: Não Informado pela instituição
Tipo de documento: Dissertação
Tipo de acesso: Acesso aberto
Idioma: por
Instituição de defesa: Universidade Federal de Santa Maria
Brasil
Física
UFSM
Programa de Pós-Graduação em Física
Centro de Ciências Naturais e Exatas
Programa de Pós-Graduação: Não Informado pela instituição
Departamento: Não Informado pela instituição
País: Não Informado pela instituição
Palavras-chave em Português:
Link de acesso: http://repositorio.ufsm.br/handle/1/21123
Resumo: In conventional superconductors described by the Bardeen-Cooper-Schrieffer (BCS) Theory, the transition from the normal to the superconducting state is accompanied by a reduction in the potential energy and an increase in the kinetic energy. On the other hand, in high-temperature superconductors the potential and the kinetic energies present an unconventional behavior that may be strongly related to the pseudogap phenomena. In this work, the kinetic and potential energies in the superconducting state of the two-dimensional Hubbard model were analyzed. The model is investigated using the Green’s function method within a n-pole approximation, which allows superconductivity with dx2�����y2-wave pairing. In the present scenario, a pseudogap emerges near the anti-nodal points in the Fermi surface, when the strong coupling regime is reached. The results show that in the low doping region, the system enters the strong coupling regime and the opening of a pseudogap is followed by a decrease in the kinetic energy and an increase in the potential energy. A phase diagram of Coulomb interaction U versus the occupation nT is also presented. This phase diagram shows clearly that the pseudogap regime coincides with the strong coupling regime in which the kinetic and potential energies present an unconventional behavior. The analysis of the density of states and the chemical potential showed that the unconventional behavior of the potential and kinetic energies occurs due to the pseudogap emergence in the high occupancy region. It was also observed that the pseudogap emergence, when the occupancy increases, is preceded by a change in the Fermi surface topology, which characterizes a Lifshitz transition. Both the pseudogap and the Lifshitz transition are affected by the next-nearest neighbor hopping t2 (of the Hubbard model). This result is in accordance with recent theoretical and experimental results for the Hubbard model and the cuprates.