On Superconducting Double Transition in PrOs₄Sb₁₂

Abstract

Superconducting double transition in PrOs_4_Sb_12 is investigated by\nanalyzing the anisotropy of the upper critical field H_c2 in the ab-plane, and\nthe possible pairing state is discussed. When mixing due to gradient coupling\nis active, the twofold-symmetric component is necessarily induced in the\nfourfold symmetric phase, leading to the twofold oscillation of H_c2, contrary\nto the experimental result. To avoid the mixing effect, the weak spin-orbit\ncoupling triplet pairing state is considered as a likely pairing function,\nwhere time-reversal symmetry is broken.\n