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Study of Vortex Motion by Thermomagnetic Effects in High Temperature Superconductors

高温超导体中热磁效应涡旋运动的研究

基本信息

批准号：
07454243
负责人：
KOBAYASHI Norio
金额：
$ 0.7万
依托单位：
Tohoku University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1995
资助国家：
日本
起止时间：
1995 至 1997
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-07454243/
关键词：
High Tc oxide superconductor Vortex motion Thermomagnetic effect Nernst effect Mixed state Vortex lattice melting Disorder 酸化物高湯超伝導体酸化物高温超伝導体

项目摘要

The aim of this project is to investigate vortex motions driven by thermomagnetic effects and to clarify the phase diagram in the vortex state in high Tc superconductors. Results are as follows. 1) Thermomagnetic effect : Ettingshausen and Nernst effects of high Tc superconductors YBa2Cu3Oy, Bi2Sr2CaCu2O8+delta and La2-xSrxCuO4 have been measured for various configurations of the magnetic field with respect to the crystal axis and the direction of the vortex motion and anisotropic properties of the vortex motion and the transport energy of the moving vortex line have been obtained. Relative magnitude of the anisotoropy are explained on the basis of the effective mass model and the quasi 2 dimensional model. However, absolute value of the transport energy is in disagreement with that expected from the type II superconducting theory and the simple flux flow model. This remains to be solved. 2) Phese diagram in the vortex state : Untwinned YBa_2Cu_3O_y single crystals have been prepared by heating twinned single crystals under an uniaxial stress. Magnetization and electrical resistance measurements on untwinned single crystals have been preformed in the magnetic fields up to 30 T using a Hall probe magnetometry. The anomalous second peak on the magnetization hysteresis curve is observed near the critical point of the first order vortex lattice melting transition. This anomalous behavior is attributed to the field-driven transition from the ordered Bragg glass to the disordered vortex glass phases. The field-driven transition is suppressed by increasing disorder introduced by electron radiation.

本课题的目的是研究热磁效应驱动下的涡旋运动，并澄清高温超导体涡旋状态下的相图。结果如下：1)热磁效应：测量了高Tc超导体YBa2Cu3Oy、Bi2Sr2CaCu2O8+delta和La2-xSrxCuO4在不同磁场配置下相对于晶轴和涡旋运动方向的Ettingshausen和能思效应，得到了涡旋运动的各向异性和运动涡旋线的输运能。在有效质量模型和准二维模型的基础上解释了各向异性的相对大小。然而，输运能量的绝对值与II型超导理论和简单通量流模型所期望的值不一致。这个问题有待解决。2)涡旋状态下的相图：在单轴应力下加热孪晶单晶制备了未孪晶YBa_2Cu_3O_y单晶。利用霍尔探头磁强计，在高达30t的磁场中对非孪晶单晶进行了磁化和电阻测量。在一阶涡晶格熔化跃迁临界点附近，磁滞曲线上出现了反常的第二峰。这种异常行为归因于场驱动从有序布拉格玻璃到无序涡旋玻璃相的转变。由电子辐射引入的无序增加抑制了场驱动跃迁。