First-Order Superconducting Transition of Sr2RuO4

TL;DR

This study uses the magnetocaloric effect to demonstrate that Sr2RuO4 undergoes a first-order superconducting-normal transition at low temperatures and specific magnetic field orientations, challenging conventional understanding.

Contribution

It provides thermodynamic evidence of a first-order transition in Sr2RuO4, suggesting a new mechanism for magnetic field-induced superconductivity suppression.

Findings

First-order S-N transition below 0.8 K near in-plane magnetic fields

Entropy release at 0.2 K is 10% of normal-state entropy

Contrasts with second-order transitions in typical type-II superconductors

Abstract

By means of the magnetocaloric effect, we examine the nature of the superconducting-normal (S-N) transition of Sr2RuO4, a most promising candidate for a spin-triplet superconductor. We provide thermodynamic evidence that the S-N transition of this oxide is of first order below approximately 0.8 K and only for magnetic field directions very close to the conducting plane, in clear contrast to the ordinary type-II superconductors exhibiting second-order S-N transitions. The entropy release across the transition at 0.2 K is 10% of the normal-state entropy. Our result urges an introduction of a new mechanism to break superconductivity by magnetic field.