Consequences of Deep Gap Minima in SrRuO for Thermal Transport

There exists an apparent conflict in experiments on unconventional superconductor Sr2RuO4 concerning the nature of the superconducting order parameter. In particular, despite evidence of chiral p-wave pairing from various experiments, thermal conductivity measurements show quasiparticle transport down to T_c/30 suggesting the existence of gap nodes. To quantify the import of this observation, we solve self-consistent BdG equations with dilute unitary scatterers to determine various low-energy properties including density of states, inverse participation ratio, and thermal conductivity. Although chiral p-wave cannot generically exhibit a true gap node, the gap structure obtained for a two-band quasi-1D model from weak-coupling RG has an anisotropic gap with deep minima. We compare our results with d-wave and anisotropic s-wave (which both have true nodes) and find a filling in of zero energy density of states for both d-wave and chiral p-wave in contrast to anisotropic s-wave. These results are augmented with a calculation of thermal conductivity using self-consistent T-matrix approximation, and together suggest anisotropic chiral p-wave cannot be ruled out by recent thermal conductivity measurements, though angle dependence may provide additional insight into the pairing symmetry.