title: In-plane anisotropy of upper critical field in Sr2RuO4
abstract: We investigated the behavior of the spin-triplet superconductor Sr2RuO4 ( T(c) approximately 1.5 K) under the magnetic fields parallel to the quasi-two-dimensional plane. The upper critical field H(c2) exhibits a clear fourfold anisotropy of about 3% at 0.35 K. Furthermore, we detected an additional transition feature below H(c2) in both the ac susceptibility and the specific heat. These second-transition features as well as the pronounced in-plane H(c2) anisotropy disappear above 0.8 K or under intentional field misalignment of less than 1 degrees. Most of these characteristics are consistent with the predicted emergence of the second superconducting phase with a line-node gap.
authors.affiliation: Department of Physics, Kyoto University, Kyoto 606-8502, Japan and Core Research for Evolutional Science and Technology of Japan Science and Technology Corporation (CREST-JST), Kawaguchi, Saitama 332-0012, Japan.
authors.initials: ZQ
authors.lastname: Mao
authors.initials: Y
authors.lastname: Maeno
authors.initials: S
authors.lastname: NishiZaki
authors.initials: T
authors.lastname: Akima
authors.initials: T
authors.lastname: Ishiguro