Phase transition in the 3 Kelvin phase in the eutectic Sr2RuO4-Ru

TL;DR

This paper investigates the interface superconducting phases in Sr2RuO4-Ru eutectic systems around 3 Kelvin, revealing two distinct phases with different symmetry properties and their impact on critical current behavior.

Contribution

It identifies and characterizes two superconducting phases at the Sr2RuO4-Ru interface, including a transition that explains anomalous critical current phenomena.

Findings

Two superconducting phases are identified between 1.5K and 3K.

A first-order transition to a time-reversal symmetry-breaking phase occurs.

The phase transition explains the sign-dependent critical current observed experimentally.

Abstract

The inhomogeneous 3-Kelvin (3K) phase of the eutectic Sr2RuO4 with Ru inclusions nucleates superconductivity at the interface between Ru and Sr2RuO4. The structure of the interface state and its physical properties are examined here. Two superconducting phases are identified between the transitions to the bulk phase at 1.5K and to the 3K phase. The nucleation of the 3K phase results in a state conserving time reversal symmetry, which generates an intrinsically frustrated superconducting network in samples with many Ru inclusions. At a lower temperature (>1.5K), a discontinuous (first order) transition to an interface state breaking time reversal symmetry is found leading to an unfrustrated network phase. It is shown that this phase transition located at a temperature between 1.5 and 3K would yield the anomalous property that the critical current in such a network depends on the sign of the current, reproducing recent experimental observations.