Thermal conductivity of superconducting Sr₂RuO₄ in oriented magnetic fields

We report in-plane thermal conductivity along [100] direction, k₁₀₀, of high quality single crystals (T_c = 1.44 K) of unconventional superconductor Sr₂RuO₄. Measurements were performed as a function of temperature T and magnetic fields H of various orientations. Linear decrease of k₁₀₀/T in T in zero field is found below 1 K, in contrast to nearly constant value in the normal state. Field dependence of k₁₀₀/T at 0.3 K in H perpendicular to the plane is qualitatively similar to that for a line-node superconducting state in the low temperature limit. The dependence gives μ₀H_c1≈8 mT and μ₀H_c2≈60 mT. In the in-plane fields, the field dependence at low temperatures shows a notable difference from the perpendicular field case. The temperature and field domain of this anomalous behavior is consistent with the existence of another superconducting phase, as proposed recently.