Simultaneous investigation of shear modulus and torsional resonance of solid 4He

TL;DR

This study simultaneously measures shear modulus and torsional resonance in solid helium-4 to understand their relationship, revealing anisotropic responses linked to grain boundaries and drive amplitude effects.

Contribution

It introduces a method to directly compare shear modulus and torsional resonance in solid helium-4, highlighting anisotropic effects and grain boundary influences.

Findings

Discrepancy in drive amplitude dependence observed.

Anisotropic response linked to low-angle grain boundaries.

Shear modulus varies with direction relative to driving force.

Abstract

We investigate the origin of a resonant period drop of a torsional oscillator (TO) containing solid ${}^{4}$He by inspecting its relation to a change in elastic modulus. To understand this relationship directly, we measure both phenomena simultaneously using a TO with a pair of concentric piezoelectric transducers inserted in its annulus. Although the temperature, ${}^{3}$He concentration, and frequency dependence are essentially the same, a marked discrepancy in the drive amplitude dependence is observed. We find that this discrepancy originates from the anisotropic response of polycrystalline solid ${}^{4}$He connected with low-angle grain boundaries by studying the shear modulus parallel to and perpendicular to the driving direction.