Squeezing superfluid from a stone: Coupling superfluidity and elasticity in a supersolid

TL;DR

This paper develops a phenomenological Landau theory linking superfluidity and elasticity in a supersolid, predicting elastic anomalies and strain effects near the phase transition in solid helium-4.

Contribution

It introduces a coupled theory of superfluidity and elasticity in supersolids, highlighting how elastic properties influence the superfluid transition and vice versa.

Findings

Elastic constants show anomalies near the transition

Superfluid transition exhibits a lambda anomaly in heat capacity

Inhomogeneous strains can broaden the transition

Abstract

In this work we start from the assumption that normal solid to supersolid (NS-SS) phase transition is continuous, and develop a phenomenological Landau theory of the transition in which superfluidity is coupled to the elasticity of the crystalline $^4$He lattice. We find that the elasticity does not affect the universal properties of the superfluid transition, so that in an unstressed crystal the well-known $\lambda$-anomaly in the heat capacity of the superfluid transition should also appear at the NS-SS transition. We also find that the onset of supersolidity leads to anomalies in the elastic constants near the transition; conversely, inhomogeneous strains in the lattice can induce local variations of the superfluid transition temperature, leading to a broadened transition.