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

利用自旋三重态超导体SnS‘和Ss’结的约瑟夫森效应，研究了UPt3和Sr2RuO4的自旋三重态超导体的有序参数，其中S、N和S‘分别是自旋三重态超导体、正常金属和S波超导体。对于垂直于c轴或b轴的UPT3表面结，通过约瑟夫森临界电流IC的磁场依赖性测试，通过改进制备工艺和降低剩余磁场，它们的质量比以前的超导体好得多。这意味着约瑟夫森电流几乎均匀地流过结，这表明约瑟夫森效应是沿b和c方向允许的。这个结果排除了顺序参数的一些候选者，例如E_&lt；2u&gt；。对于横跨a-b角的结，IC的磁场调制到目前为止还没有显示出a-b平面上的相变迹象。对于Sr2RuO4，IC沿c轴的磁场依赖关系表明，约瑟夫森电流只流过结的限制区，尽管结的面积只有10^&lt；-5&gt；cm^2，它是在垂直于c轴的解理平面上形成的，没有台阶和Ru片层。目前还不清楚是否允许与d矢量方向有关的c轴约瑟夫森耦合。

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.