Tests of anisotropic superconductivity using Josephson interferometers

本文利用Josephson结研究了重费米子超导体UPt_3、CeIrIn_5和CePt_3Si的各向异性序参量，特别是Josephson干涉仪可以检测到两个方向间序参量的相位差。垂直于a[112^^-0]和b[101^^-0]轴的UPt_3上的角结迄今尚未显示出指示顺序参数在a和b轴方向之间相移的行为。即使考虑到角结的几何不对称性，该结果也与UPt_3中order参数的二维E_<2u>场景相矛盾。单晶CeIrIn_5和s波超导体之间的约瑟夫森临界电流的磁场调制在[100]方向上显示出接近理想的弗劳恩霍夫模式，在[110]方向上与该模式有很小的偏差。在（100）和（010）表面的角结上，d波超导的迹象没有被清楚地观察到，可能是由于结的不对称性。在单晶CePt_3Si和Al之间的I_c的磁场依赖性中，到目前为止，仅在a轴面上的结处观察到零场的主导最大峰，这表明至少对于平行于a轴的电流是允许约瑟夫森效应的。c轴表面结的随机振荡模式可归因于非中心对称超导体中的磁通捕获或时间反转对称性的破坏。

The anisotropic order parameters of heavy-fermion superconductors have been investigated for UPt_3, CeIrIn_5 and CePt_3Si using Josephson junctions, especially Josephson interferometers that can detect the phase difference of the order parameter between two directions.The corner junction on the UPt_3 faces perpendicular to the a[112^^-0] and b[101^^-0] axes has not shown a behavior indicating the phase shift of the order parameter between the a- and b-axis directions thus far. Even if the geometric asymmetry of the corner junction is taken into account, this result contradicts, for example, the two-dimensional E_<2u> scenario for the order parameter in UPt_3.The magnetic-field modulation of the Josephson critical current between a single-crystal CeIrIn_5 and an s-wave superconductor has shown a nearly ideal Fraunhofer pattern in the [100] direction and a small deviation from that pattern in the [110] direction. The indication of the d-wave superconductivity has not been observed clearly for the corner junction on the (100) and (010) faces, probably because of the asymmetry of the junction.In the magnetic-field dependence of I_c between a single crystal CePt_3Si and Al, a dominant maximum peak at zero field has been observed only for the junction on the a-axis face thus far, indicating that the Josephson effect is allowed at least for current flow parallel to the a axis. The randomly oscillating pattern for the junction on the c-axis face may be ascribed to the magnetic-flux trapping or the broken time-reversal symmetry in noncentrosymmetric superconductors.