Elastocaloric determination of the phase diagram of Sr$_2$RuO$_4$

TL;DR

This study maps the phase diagram of Sr$_2$RuO$_4$ using elastocaloric effect measurements, revealing entropy changes and phase boundaries in both normal and superconducting states, advancing understanding of its unconventional superconductivity.

Contribution

First high-precision elastocaloric study of Sr$_2$RuO$_4$ covering both normal and superconducting states, providing detailed phase diagram and entropy insights.

Findings

Strong entropy quench upon entering superconductivity

Quantitative estimate of entropy change near magnetic phase

Phase diagram shows similarities and unique features compared to other unconventional superconductors

Abstract

One of the main developments in unconventional superconductivity in the past two decades has been the discovery that most unconventional superconductors form phase diagrams that also contain other strongly correlated states. Many systems of interest are therefore close to more than one instability, and tuning between the resultant ordered phases is the subject of intense research1. In recent years, uniaxial pressure applied using piezoelectric-based devices has been shown to be a particularly versatile new method of tuning, leading to experiments that have advanced our understanding of the fascinating unconventional superconductor Sr$_2$RuO$_4$. Here we map out its phase diagram using high-precision measurements of the elastocaloric effect in what we believe to be the first such study including both the normal and the superconducting states. We observe a strong entropy quench on entering the superconducting state, in excellent agreement with a model calculation for pairing at the Van Hove point, and obtain a quantitative estimate of the entropy change associated with entry to a magnetic state that is observed in proximity to the superconductivity. The phase diagram is intriguing both for its similarity to those seen in other families of unconventional superconductors and for extra features unique, so far, to Sr$_2$RuO$_4$.