Interface superconductivity in the eutectic Sr2RuO4-Ru:: 3-K phase of Sr2RuO4 -: art. no. 214519

Enhanced superconductivity in the eutectic system Sr2RuO4-Ru is referred to as the 3-K phase of the spin-triplet superconductor Sr2RuO4 because of its enhanced superconducting transition temperature T-c of similar to3 K. We have investigated the field-temperature (H-T) phase diagram of the 3-K phase for fields parallel and perpendicular to the ab plane of Sr2RuO4, using out-of-plane resistivity measurements. We have found an upturn curvature in the H-c2(T) curve for Hparallel toc, and a rather gradual temperature dependence of H-c2 close to T-c for both Hparallel toab and Hparallel toc. We have also investigated the dependence of H-c2 on the angle between the field and the ab plane at several temperatures. Fitting the Ginzburg-Landau effective-mass model apparently fails to reproduce the angle dependence, particularly near Hparallel toc and at low temperatures. We propose that all of these characteristic features can be explained, at least in a qualitative fashion, on the basis of a theory by Sigrist and Monien that assumes surface superconductivity with a two-component order parameter occurring at the interface between Sr2RuO4 and Ru inclusions. This provides evidence of the chiral state postulated for the 1.5-K phase by several experiments.