THERMAL-CONDUCTIVITY OF SUPERCONDUCTING UPT3 AT LOW-TEMPERATURES

WE study the thermal conductivity within the E(1g) and E(2u) models fo r superconductivity in UPt3 and compare the theoretical results for el ectronic heat transport with recently measured results reported by Lus sier, Ellman and Taillefer. The existing data down to T/T-c approximat e to 0.1 provides convincing evidence for the presence of both line an d point nodes in the gap, but the data can be accounted for either by an E(1g) or E(2u) order parameter. We discuss the features of the pair ing symmetry, Fermi surface, and excitation spectrum that are reflecte d in the thermal conductivity at very low temperatures. Significant di fferences between the E(1g) and E(2u) models are predicted to develop at excitations energies below the bandwidth of the impurity-induced An dreev bound states. The zero-temperature limit of the (c) over cap axi s thermal conductivity, lim(T-->0)kappa(c)/T, is universal for the E(2 u) model, but non-universal for the E(1g) model. Thus, impurity concen tration studies at very low temperatures should differentiate between the nodal structures of the E(2u) and E(1g) models.