We investigated the behavior of the spin-triplet superconductor Sr2RuO4 (Tc≈1.5 K) under the magnetic fields parallel to the quasi-two-dimensional plane. The upper critical field Hc2 exhibits a clear fourfold anisotropy of about 3% at 0.35 K. Furthermore, we detected an additional transition feature below Hc2 in both the ac susceptibility and the specific heat. These second-transition features as well as the pronounced in-plane Hc2 anisotropy disappear above 0.8 K or under intentional field misalignment of less than 1°. Most of these characteristics are consistent with the predicted emergence of the second superconducting phase with a line-node gap.
All Science Journal Classification (ASJC) codes
- Physics and Astronomy(all)