Dinâmica de vórtices em supercondutores mesoscópicos com rede de centros de aprisionamento: estudo em temperatura próxima de Tc e diferentes tipos de defeitos
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Data
2018-03-06
Autores
Okimoto, Danilo
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Universidade Estadual Paulista (Unesp)
Resumo
O estudo de materiais supercondutores (SCs) em escalas nanométricas tem se destacado na área da Física de Matéria Condensada nas últimas décadas. O foco tem-se dado aos estudos das propriedades elétricas e magnéticas desses materiais, além da intensificação do desenvolvimento de técnicas para a produção e manipulação em nanoescala. Nos ditos supercondutores mesosocópicos, efeitos de confinamento influenciam na dinâmica de vórtices, ocasionando, inclusive, estados de vórtices múltiplos e de vórtices gigantes. Neste trabalho, usamos a teoria de Ginzburg-Landau para estudar supercondutores mesoscópicos com uma rede de defeitos. Foram analisados o comportamento magnético das amostras para dois tipos diferentes de defeitos, sendo eles, buracos que transpassam o material (antidots, ADs) e buracos com uma fina camada supercondutora (Blind Holes, BHs). As amostras foram expostas a campos externos variáveis e o loop de histerese das mesmas fora levantado. Os sistemas foram simulados com temperatura T=0,9Tc, e possuindo geometria quadrada de tamanho lateral L=54 ξ(0), defeitos também quadrados de lado l=2ξ(0) e espaçados por 2ξ(0). Nestas condições, efeitos de confinamento são muito fortes, inclusive devido ao tamanho dos vórtices, cujo ξ(T=0,9) é aproximadamente 3ξ(0). Com isso, há pouca diferença no comportamento global das diferentes amostras, contudo, a dinâmica de vórtices é alterada devida à natureza distinta entre ADs e BHs. Outro fato interessante é que, sendo os vórtices muito grandes, os defeitos, embora tenham influência sobre eles, não são efetivos em seu aprisionamento, principalmente durante a primeira penetração. Com isso, em campo nulo, a magnetização das amostras é nula.
The study of superconducting materials (SCs) in nanometric scales has been outstanding in the area of Condensed Matter Physics in the last decades. The focus has been given to the study of the electrical and magnetic properties of the materials, besides the intensification of the development of techniques for nanoscale production and manipulation. In the so-called mesoscopic superconductors, confinement effects influence the dynamics of vortices, including multiple vórtices states and giant vortices. In this work, we use the Ginzburg-Landau theory to study mesoscopic superconductors with an array of defects. The magnetic behavior of the samples was analyzed for two different types of defects: holes that pass through the material (antidots, ADs) and holes with a thin superconducting layer (Blind Holes, BHs). The samples were exposed to variable external fields and the hysteresis loop of the samples had been studied. The system were simulated with temperature T=0,9Tc, and a square geometry with lateral size L=54 ξ(0), square defects with lateral size l=2ξ(0) and spaced by 2ξ(0). Under these conditions, confinement effects are very strong, including due to the size of the vortices, whose ξ(T=0,9) is approximately 3ξ(0). So, there is little difference in the overall behavior of the different samples, however, the vortex dynamics is altered due to the distinct nature of ADs and BHs. Another interesting fact is that, since the vortices are very large, the defects, although they have an influence on them, are not effective in their imprisonment, especially during the first penetration. Thus, in the null field, the magnetization of the samples is zero.
The study of superconducting materials (SCs) in nanometric scales has been outstanding in the area of Condensed Matter Physics in the last decades. The focus has been given to the study of the electrical and magnetic properties of the materials, besides the intensification of the development of techniques for nanoscale production and manipulation. In the so-called mesoscopic superconductors, confinement effects influence the dynamics of vortices, including multiple vórtices states and giant vortices. In this work, we use the Ginzburg-Landau theory to study mesoscopic superconductors with an array of defects. The magnetic behavior of the samples was analyzed for two different types of defects: holes that pass through the material (antidots, ADs) and holes with a thin superconducting layer (Blind Holes, BHs). The samples were exposed to variable external fields and the hysteresis loop of the samples had been studied. The system were simulated with temperature T=0,9Tc, and a square geometry with lateral size L=54 ξ(0), square defects with lateral size l=2ξ(0) and spaced by 2ξ(0). Under these conditions, confinement effects are very strong, including due to the size of the vortices, whose ξ(T=0,9) is approximately 3ξ(0). So, there is little difference in the overall behavior of the different samples, however, the vortex dynamics is altered due to the distinct nature of ADs and BHs. Another interesting fact is that, since the vortices are very large, the defects, although they have an influence on them, are not effective in their imprisonment, especially during the first penetration. Thus, in the null field, the magnetization of the samples is zero.
Descrição
Palavras-chave
TDGL, Pinning centers, Mesoscopic superconductors, Supercondutividade