Field–temperature phase diagram of the 3-K phase of Sr2RuO4

We have investigated the field–temperature phase diagram of the 3-K phase (Sr2RuO4–Ru eutectic) for two field directions (H∥ab and H∥c) using resistivity data. We have found an upturn curvature in the Hc2(T) curve for H∥c and a rather gradual temperature dependence of Hc2 close to Tc. We propose that these characteristic features can be explained, at least in a qualitative fashion, on the basis of a theory that assumes surface superconductivity with a two-component order parameter at the interface between Sr2RuO4 and Ru inclusions.