Non-linear Elastic Response in Solid Helium: critical velocity or strain

TL;DR

This study investigates the non-linear elastic response of solid helium-4, revealing that the shear modulus depends on stress magnitude rather than velocity, challenging the interpretation of supersolidity as a velocity-dependent phenomenon.

Contribution

It demonstrates that the elastic response in solid helium-4 is stress-dependent, providing new insights into dislocation dynamics and questioning the velocity-based explanation of supersolidity.

Findings

Shear modulus depends on stress, not velocity.

Dislocation motion explains the non-linear elastic behavior.

Results challenge the velocity-based supersolidity interpretation.

Abstract

Torsional oscillator experiments show evidence of mass decoupling in solid 4He. This decoupling is amplitude dependent, suggesting a critical velocity for supersolidity. We observe similar behavior in the elastic shear modulus. By measuring the shear modulus over a wide frequency range, we can distinguish between an amplitude dependence which depends on velocity and one which depends on some other parameter like displacement. In contrast to the torsional oscillator behavior, the modulus depends on the magnitude of stress, not velocity. We interpret our results in terms of the motion of dislocations which are weakly pinned by 3He impurities but which break away when large stresses are applied.