Interface superconductivity in the eutectic Sr2RuO4-Ru: 3-K phase of Sr2RuO4

TL;DR

This study investigates the magnetic field-temperature phase diagram of the Sr2RuO4-Ru eutectic system's 3-K phase, revealing surface superconductivity and supporting the chiral state hypothesis for this unconventional superconductor.

Contribution

It provides experimental evidence of surface superconductivity and tests the applicability of the Sigrist and Monien model to the 3-K phase of Sr2RuO4-Ru.

Findings

Upturn curvature in Hc2(T) for H // c

Gradual Hc2(T) dependence near Tc

Failure of Ginzburg-Landau model to fit angle dependence

Abstract

The eutectic system Sr2RuO4-Ru is referred to as the 3-K phase of the spin-triplet supeconductor Sr2RuO4 because of its enhanced superconducting transition temperature Tc of ~3 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 Hc2(T) curve for H // c, and a rather gradual temperature dependence of Hc2 close to Tc for both H // ab and H // c. We have also investigated the dependence of Hc2 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 H // c and at low temperatures. We propose that all of these charecteric 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.