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Effects of Layer Structure in High Temperature Superconducting Oxides

高温超导氧化物中层结构的影响

基本信息

批准号：
03640328
负责人：
TACHIKI Masashi
金额：
$ 1.15万
依托单位：
Tohoku University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1991
资助国家：
日本
起止时间：
1991 至 1992
项目状态：
已结题

项目摘要

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.

基于由强超导层和弱超导层组成的层状模型，研究了层状结构对高温超导氧化物超导性能的影响。本文指出，在这类层状氧化物中，输运电流主要在强超导层中流动，而涡旋中心位于弱超导层中，作用在涡旋上的Lorents力与涡旋中心处的输运电流成正比，从而使作用在涡旋上的有效驱动力大大减小，我们估算了钉扎力和临界电流，本文还利用磁通流模型研究了这类氧化物的电阻状态，并从唯象的角度计算了外场作用下电阻率随温度的变化关系。结果表明，在氧化物的电阻转变过程中，发生了从热辅助磁通流区向磁通流主导区的过渡，当超导相干长度小于层厚时，层状超导体中的上临界场H_的角度依赖<c2>性与各向异性有效质量模型和薄膜中的上临界场H_的角度依赖性明显不同。本文用层状超导体的广义Ginzburg-Landau模型计算了任意方向reta上的上临界场，在<c2>reta =90 °附近（平行于层）H_（90 °）的角度依赖关系与H_（90 °）的温度依赖关系的维数有关<c2>。我们在3D区域中在转变温度附近有一个钟形曲线，在2D区域中在H_vs. rheta曲线中在rheta=90 ℃处有一个尖点<c2>。