Dinâmica de vórtices em sistemas supercondutores mesoscópicos do tipo I e do tipo II
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Data
2023-01-25
Autores
Presotto, Alice
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
Avanços na tecnologia de nanofabricação tem possibilitado o desenvolvimento de materiais em escala mesoscópica, da ordem de algumas dezenas de nanômetros. Nessas escalas, a dinâmica de vórtices é fortemente dominada por efeitos de confinamento. Dessa forma, a investigação de suas características tem importância fundamental para o desenvolvimento e aplicação desses materiais de forma eficaz, pois há uma mudança significativa nos parâmetros críticos. Assim, neste trabalho foram estudados supercondutores do tipo I e do tipo II com interesse na dinâmica e comportamento da matéria de vórtices em vários tipos de sistemas mesoscópicos. Utilizando as equações de Ginzburg-Landau dependentes do tempo tridimensionais, foi simulado um filme fino supercondutor do tipo I com um gradiente de temperatura. Mostramos que a formação de clusters de vórtices é favorecida, e que está relacionada com à interação vórtice-vórtice não monotônica. Fazendo uso da mesma teoria, foi simulado um supercondutor do tipo I com gradiente de espessura, onde verificamos que tal formato induz uma organização assimétrica das correntes supercondutoras no interior da amostra, o que favorece uma organização irregular dos vórtices e uma resposta paramagnética da magnetização, M(H), para o ramo descendente do campo aplicado. Também foi estudado, por meio das equações generalizadas de Ginzburg-Landau dependentes do tempo, uma fita supercondutora infinitamente longa do tipo II, com grãos espaçados por weak-links. As amostras foram submetidos a campos magnéticos externos e campos elétricos, o que originou regimes de movimentos (flux-flow) distintos dentro da fita. Ainda utilizando a teoria generalizada, foi simulado um supercondutor do tipo II contendo constrição mesoscópica, onde estudou-se a dinâmica de vórtices cinemáticos, no qual foi elaborado um diagrama de fases Jtr(H) (corrente de transporte por campo) que compreende os estados resistivos encontrados na amostra supercondutora. Os trabalhos brevemente citados são desenvolvidos em maiores detalhes na sequência, onde, para cada Capítulo, é apresentado um resumo mais extenso referente ao seu conteúdo.
Advances in nanofabrication technology have enabled the development of materials on a mesoscopic scale, from order of a few tens of nanometers. At these scales, the vortex dynamics is strongly dominated by confinement effects. Thus, the investigation of their characteristics are fundamental important for the development and application of these materials effectively, as there is a significant change in the critical parameters. Thus, in this work type I and type II superconductors were studied with interest in the dynamics and behavior of the vortex matter in various types of mesoscopic systems. Using the threedimensional time-dependent Ginzburg-Landau equations, a type I superconducting thin film with a gradient of temperature was simulated. We show that the development of clusters of vortices is favored, and we show that this related with no-monotonic vortex-vortex interaction. Making use of the same theory, a type I superconductor with a gradient of thickness was simulated, where we verified that such system induces an asymmetrical organization of the superconducting currents inside the sample, which favors an irregular configuration of the vortices and a paramagnetic magnetization response, M(H) , for the descending branch of the applied field. It was also studied, by means of the generalized time-dependent Ginzburg-Landau equations, an infinitely long type II superconducting strip, with grains spaced by weak-links. The samples were submitted to external magnetic fields and electric fields, which gave rise to movement regimes (flux-flow) within the tape. Still using the generalized theory, a type II superconductor containing mesoscopic constriction was simulated, where the dynamics of kinematic vortices were studied, in which a phase diagram Jtr(H) was elaborated, comprising the resistive states found in the superconducting sample. The briefly cited works are developed in greater detail in the sequence, where, for each Chapter, a more extensive abstract is presented regarding its content.
Advances in nanofabrication technology have enabled the development of materials on a mesoscopic scale, from order of a few tens of nanometers. At these scales, the vortex dynamics is strongly dominated by confinement effects. Thus, the investigation of their characteristics are fundamental important for the development and application of these materials effectively, as there is a significant change in the critical parameters. Thus, in this work type I and type II superconductors were studied with interest in the dynamics and behavior of the vortex matter in various types of mesoscopic systems. Using the threedimensional time-dependent Ginzburg-Landau equations, a type I superconducting thin film with a gradient of temperature was simulated. We show that the development of clusters of vortices is favored, and we show that this related with no-monotonic vortex-vortex interaction. Making use of the same theory, a type I superconductor with a gradient of thickness was simulated, where we verified that such system induces an asymmetrical organization of the superconducting currents inside the sample, which favors an irregular configuration of the vortices and a paramagnetic magnetization response, M(H) , for the descending branch of the applied field. It was also studied, by means of the generalized time-dependent Ginzburg-Landau equations, an infinitely long type II superconducting strip, with grains spaced by weak-links. The samples were submitted to external magnetic fields and electric fields, which gave rise to movement regimes (flux-flow) within the tape. Still using the generalized theory, a type II superconductor containing mesoscopic constriction was simulated, where the dynamics of kinematic vortices were studied, in which a phase diagram Jtr(H) was elaborated, comprising the resistive states found in the superconducting sample. The briefly cited works are developed in greater detail in the sequence, where, for each Chapter, a more extensive abstract is presented regarding its content.
Descrição
Palavras-chave
Supercondutores mesoscópicos, GTDGL, Dinâmica de vórtices, Gradiente térmico, Cunha, Weak-link, Flux-flow, Constrição, Mesoscopic superconductors, Vortex dynamics, Thermal gradient, Wedge, Weak-link, Flux-flow, Constriction