Tests of anisotropic superconductivity using Josephson interferometers

点击翻译按钮获取中文摘要

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.