Evidence for weak spin-orbit interaction experienced by Cooper pairs in the spin-triplet superconductor UPt; Pt-NMR study

Aoyama, Taisuke*; Kotegawa, Hisashi*; Kimura, Noriaki*; Yamamoto, Etsuji  ; Haga, Yoshinori   ; Onuki, Yoshichika*; To, Hideki*

Pt-NMR measurements under magnetic field () parallel to the -axis in the vicinity of the upper critical field have been carried out on the heavy-fermion superconductor UPt. The quasiparticle spin susceptibility was obtained from the measurements. The field dependence of the susceptibility suggests that the -vector freely rotates in magnetic field. It is therefore concluded that spin-orbit interaction, which confines the direction of the -vector with respect to the crystal axis, is weak in UPt.