Estudo do efeito nernst em supercondutores de alta temperatura crítica(HTSC)

• Ano de defesa: 2005
• Autor(a) principal: Dias, Daniel Henrique Nogueira
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Programa de Pós-graduação em Física; Física
• Palavras-chave em Português: Supercondutor de alta temperatura; Vórtices Supercondutores.; CNPQ::CIENCIAS EXATAS E DA TERRA::FISICA
• Link de acesso: https://app.uff.br/riuff/handle/1/18695

A central issue of high temperature superconductors (HTSC) is the connection of normal state correlations, referred as the pseudogap, to the origins of high Tc. The big question is whether the pseudogap, which manifests in many different forms but usually is presented, as it is seen in tunneling experiments, as a depletion of the quasiparticle density of states below a characteristc temperature T¤, has to have or not with the superconductivity. A very interesting and puzzling experiment is the Nernst effect in the normal state above Tc. It shows a drifting of the vortices which usually occurs in normal superconductors only below Tc. Our assuption is that it is meassured above Tc for HTSC because these material are inhomogeneous. As the HTSC present a local variation in the charge density, it has a distribution of local critical temperatures. The onset of the Nernst signal is the onset of superconductivity (T¤ that it is the greater of Tc(ri)) in isolatades islands and the superconducting or resistive transistion occurs when the superconducting islands percole. We calculate the onset of superconductivity by two methods: Firstly we use a BCS formalism, governed by a Hubbard Hamiltonian, to derive the dependence of T¤ with the doping level. Than we use a BdG formalism which has the advantage to make local calculations in a mesh with finite size. We show that our derived phase diagram can be in good agreement with experimental data.