Identification of nonunitary triplet pairing in a heavy Fermion superconductor UPt3

A NMR experiment recently done on a heavy Fermion superconductor UPt3 is interpreted in terms of a nonunitary spin-triplet pairing state which we have been advocating. The proposed state successfully explains various aspects of the seemingly complicated Knight shift behaviors probed for major orientations, including a remarkable d-vector rotation under weak fields. This makes UPt3 the first example of a charged many-body system forming a spin-triplet odd-parity pairing at low temperatures, which demonstrates definitively that the putative spin-orbit coupling in UPt3 is weak. (author)