Estudos sobre o comportamento não-convencional de supercondutores cupratos de alta temperatura crítica

• Autor(a) principal: Kasal, Raphael Barata
• Data de Publicação: 2011
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: Repositório Institucional da Universidade Federal Fluminense (RIUFF)
• Texto Completo: https://app.uff.br/riuff/handle/1/19338
• topic: Supercondutividade; Cupratos; Pseudogap; Desordem eletrônica; Modelo de Bogoliubov-de Gennes; Magnetização; Modelo do Estado Crítico; CNPQ::CIENCIAS EXATAS E DA TERRA::FISICA

While low temperature superconductors have metallic normal phases that are well characterized, the normal phase of the high Tc cuprates present many unconventional properties that still demand a global and more comprehensive explanation. Among these anomalous properties, which strongly depend on the doping level (p) of the material, are the universal behavior of the Tc x p curve of the phase diagram of the cuprates and the persistence of local gaps in temperatures well above Tc, observed in tunneling conductance curves for STM (Scanning Tunneling Microscope) measurements. The nature of these gaps above Tc, which are known in the literature as pseudogaps, is a matter of intense debate without a consensus, so far, that says if its detection is independent of superconductivity or not or even if there is more then one type of pseudogap. As for the magnetization curves of these materials, different teams have detected the appearance of a precursor diamagnetic response above the superconducting transition temperature in bulk samples. Moreover, nuclear quadrupole resonance (NQR) experiments have shown strong indications that the superconducting cuprates are highly non-homogeneous, with intrinsic eletronic disorder appearing along the conduction planes as, for exemple, the so-called stripes phase. This thesis aims to study these anomalous behaviours, using the phenomenological approach of the Critical State models to investigate the precursor diamagnetism of the cuprates and the Bogoliubov-de Gennes theory for the phase diagram of these materials, including the pseudogap phase.The results obtained for systems with non-homogeneous distribution of charge enable the formulation of a unique and coherent picture that might explain the anomalous behavior of superconducting cuprates.