In-plane anisotropy of upper critical field in Sr2RuO4

摘要: We investigated the behavior of spin-triplet superconductor Sr2RuO4 ( T(c) approximately 1.5 K) under magnetic fields parallel to quasi-two-dimensional plane. The upper critical field H(c2) exhibits a clear fourfold anisotropy about 3% at 0.35 K. Furthermore, we detected an additional transition feature below in both ac susceptibility and specific heat. These second-transition features as well pronounced in-plane disappear above 0.8 K or intentional misalignment less than 1 degrees. Most these characteristics are consistent with predicted emergence second superconducting phase line-node gap.