Nonunitary Spin-Triplet Superconductivity inUPt3: Evidence fromP195

1Department of Physical Science, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531 2Department of Physics, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan 3Advanced Science Research Center, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195, Japan 4Faculty of Engineering, Toyama Prefectural University, Toyama 939-0398, Japan (Received 4 September 1997 ) 195Pt Knight shift (KS) measurements covering the superconducting multiple phases for major field (H) orientations have been carried out on the high-quality single crystal UPt 3. For H . 5 kOe, the KS does not change below the superconducting transition temperature Tc down to 28 mK, regardless of major crystal orientations, which provides evidence that the odd-parity superconductivity with the parallel spin pairing is realized. By contrast, the KSdecreasesbelow Tc for Hb k b axis and Hb , 5 kOe and forHc k c axis andHc , 2.3 kOe, whereas the KS for Ha k a axis isT independent acrossTc down to Ha , 1.764 kOe. These novel findings entitle UPt 3 as the first spin-triplet oddparity superconductor including a nonunitarypairing characterized by the two-component d vector like db 1 idc at low T and lowH. [S0031-9007(98)05803-7]