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Studies of the order parameter for spin-triplet superconductors using the Josephson effect

利用约瑟夫森效应研究自旋三重态超导体的序参数

基本信息

批准号：
14540343
负责人：
SUMIYAMA Akihiko
金额：
$ 2.37万
依托单位：
Himeji Institute of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2002
资助国家：
日本
起止时间：
2002 至 2003
项目状态：
已结题

项目摘要

The order parameter of spin-triplet superconductors, which is described in terms of the d-vector, has been investigated for UPt_3 and Sr_2RuO_4 using the Josephson effect of SNS' and SS' junctions, where S, N and S' are a spin-triplet superconductor, a normal metal and an s-wave superconductor, respectively.As for the junctions made on the UPt_3 surface perpendicular to the c-or b-axis, the quality of them, which is tested in the magnetic field dependence of the Josephson critical current Ic, has become much better than the previous ones by improving the fabrication process and decreasing the residual magnetic field. This means that the Josephson current flows almost uniformly through the junction, suggesting that the Josephson effect is allowed along b and c directions. This result excludes some of the candidates for the order parameter, such as E_<2u>. The magnetic field modulation of Ic for the junctions straddling the a-b corner has indicated no sign of the phase change in the a-b plane so far.In the case of Sr_2RuO_4, the magnetic field dependence of Ic along the c-axis suggests that the Josephson current flows through only the restricted region of the junction, although the junctions, of which area is as small as 10^<-5> cm^2 was fabricated on the cleaved flat surface perpendicular to the c-axis, which is free of steps and Ru lamellas. It is stili not clear whether the c-axis Josephson coupling, which relates to the direction of the d-vector, is allowed or not.

利用SNS结和SS结的Josephson效应，研究了UPt_3和Sr_2RuO_4的自旋三重态超导体的序参量，其中S、N和S′分别是自旋三重态超导体、正常金属超导体和S波超导体。对于垂直于c轴或b轴的UPt_3表面制作的结，通过改进制作工艺和减小残余磁场，在约瑟夫森临界电流Ic的磁场依赖性测试中，其质量大大优于之前的结。这意味着约瑟夫森电流几乎均匀地流过结，表明约瑟夫森效应沿着b和c方向是允许的。该结果排除了order参数的一些候选项，例如E_<2u>。横跨a-b角的结的Ic的磁场调制到目前为止还没有显示a-b平面的相位变化的迹象。在Sr_2RuO_4中，Ic沿c轴的磁场依赖性表明Josephson电流仅流经结的限制区域，尽管结的面积小至10^<-5> cm^2，是在垂直于c轴的切割平面上制作的，没有台阶和Ru片层。与d矢量方向有关的c轴Josephson耦合是否允许尚不清楚。