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

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.