Field-temperature phase diagram of Sr2RuO4–Ru eutectic Original Research Article

We have investigated the out-of-plane resistivity of Sr2RuO4–Ru eutectic, which exhibits interface superconductivity with an enhanced transition temperature Tc of about 3 K. We present the detailed field-temperature (H–T) phase diagram for fields parallel and perpendicular to the RuO2 planes of Sr2RuO4. The behavior of both H–T curves around Tc is well described as Hc2∝(Tc−T)n, where n=0.62 (H//ab) and n=0.66 (H//c). The theoretically expected value 0.5, based on the model assuming a flat Sr2RuO4–Ru boundary with an enhanced interaction between electrons, is in reasonable agreement with the observation. In addition, the H–T curve for H//c exhibits a positive curvature at lower temperatures. It is theoretically predicted that the coupling of the two order parameter components, not degenerate, can cause an increase in Hc2, especially strong in the out-of-plane field direction. The observed variation of the curvature is in accord with this theoretical picture.