Effects of Layer Structure in High Temperature Superconducting Oxides

点击翻译按钮获取中文摘要

Based on a layered model composed of strongly and weakly superconducting layers,we investigated the effects of the layer structure on the superconducting properties of the high temperature superconducting oxides. It has been pointed out that the transport current in these layered oxides flows mainly in the strongly superconducting layers, while the vortex center lies in a weakly superconducting layer.The Lorents force working on the vortex is proportional to the value of the transport current at the vortex center.As a result,the effective driving force acting on the vortex is greatly reduced.We estimated the pinning force and the critical current,using this layered model.The resistive state in these oxides was also investigated,based on a flux flow model.We calculated phenomenologically the temperature dependence of the resistivity under an external field. It is concluded that in the resistive transition of the oxides a crossover from thermally assisted flux flow regime to flux flow dominated regime takes place.The angular dependence of the upper critical field H_<c2> in layered superconductors shows a clear difference from that in the anisotropic effective mass model and also from that in a thin film when the superconducting coherence length perpendicular the layers is shorter than the layer thickness at T=0K.We formulated a calculation of the upper critical field in an arbitrary direction rheta, using a generalized Ginzburg-Landau model for layered superconductors.The angular dependence of H_<c2> in the region near rheta=90ﾟ(parallel to the layers)is correlated with the dimensionality in the temperature dependence of H_<c2>(90ﾟ). We have a bell-shaped curve in the 3D regime near the transition temperature and a curve with a cusp at rheta=90ﾟ in the 2D regime in the H_<c2> versus rheta curve.