Thermal Conductivity near H_c2 for spin-triplet superconducting States with line nodes in Sr_2RuO_4

Abstract

We calculate the thermal conductivity kappa in magnetic fields near H_c2 for spin-triplet superconducting states with line nodes vertical and horizontal relative to the RuO_2-planes. The method for calculating the Green's functions takes into account the spatial variation of the order parameter and superconducting flow for the Abrikosov vortex lattice. For in-plane magnetic field we obtain variations of the in-plane kappa with two-fold symmetry as a function of rotation angle where the minima and maxima occur for field directions parallel and perpendicular to the heat flow. The amplitude of the variation decreases with increasing impurity scattering and temperature. At higher temperatures the minima and maxima of the variation are interchanged. Since the results for vertical and horizontal line nodes are almost the same we cannot say which of the two pairing models is more compatible with recent measurements of kappa in Sr_2RuO_4. The observed four-fold modulation of kappa in YBa_2Cu_3O_(7-δ) is obtained for d-wave pairing by taking into account the particular shape of the Fermi surface and the finite temperature effect. The results for kappa for the f-wave pairing state with horizontal line nodes disagree in some respects with the measurements on UPt_3.