Orbital symmetry of a triplet pairing in a heavy Fermion superconductor UPt_3

TL;DR

This paper determines the orbital symmetry of the triplet pairing in UPt_3 using thermal conductivity and ultrasound attenuation, proposing experimental tests to distinguish between possible superconducting states.

Contribution

It identifies the orbital part of the order parameter in UPt_3 and combines it with the spin part to propose specific triplet pairing states, advancing understanding of its superconducting symmetry.

Findings

Orbital symmetry expressed by (_x(k), _y(k))

Possible non-unitary bipolar or unitary planar triplet states

Weak spin-orbit coupling allows in-plane rotation of the d-vector

Abstract

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 (\lambda_x(k), \lambda_y(k)) is combined with the previously determined triplet spin part, leading to 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 (\lambda_x(k), \lambda_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) = b \lambda_x(k) + i j \lambda_y(k) or the unitary planar state of the form: d(k) = b \lambda_x(k) + j \lambda_y(k) where b \perp j = c, or a with the hexagonal unit vectors a, b and c. The d vector is rotatable in the plane spanned by a and c perpendicular to b under weak applied c-axis field because of the weak spin orbit coupling. Experiments are proposed to distinguish between the equally possible these states.