Orbital Symmetry of a Triplet Pairing in a Heavy Fermion Superconductor UPt 3

The orbital symmetry of the superconducting order parameter in UPt 3 is identified by evaluating the directionally dependent thermalconductivity and ultrasound attenuation in the clean limit and compared with the existing data for both basal plane and the c -axis of a hexagonal crystal. The resulting two component orbital part expressed by (λ x ( k ), λ y ( k )) is combined with the previously determined triplet spin part, leading to the order parameter of either the non-unitary bipolar state of the form: \({ d}({ k})={ b̂}λ_x ({ k})+{ i}{ ĵ} λ_y({ k})\) or the unitary planar state of the form: \({ d}({ k})={ b̂}λ_x({ k})+{ ĵ} λ_y({ k})\) where \({ b̂}⊥{ ĵ} ={ ĉ}\), or \({ â}\) with the hexagonal unit vectors \({ â}\), \({ b̂}\) and \({ ĉ}\). The d vector is rotatable in the plane spanned by \({ â}\) and \({ ĉ}\) perpendicular to \({ b̂}\) under weak applied c -axis field because of the weak spin-orbit coupling. Experiments are proposed to distinguish between the equally possible these states.