Comment on "Giant Plasticity of a Quantum Crystal"

TL;DR

This paper challenges the interpretation of giant plasticity in Helium-4 quantum crystals by showing that classical thermally activated dislocation models can explain the observed phenomena without invoking quantum effects.

Contribution

It provides a classical explanation for the observed mechanical properties of Helium-4, questioning the necessity of quantum tunneling in their interpretation.

Findings

Classical dislocation glide models can explain the observed giant plasticity.

Shear modulus plateau and low dissipation can result from thermally activated processes.

Quantum tunneling is not required to account for the experimental signatures.

Abstract

In their Letter, Haziot et al. [Phys. Rev. Lett. 110 (2013) 035301] report a novel phenomenon of giant plasticity for hcp Helium-4 quantum crystals. They assert that Helium-4 exhibits mechanical properties not found in classical plasticity theory. Specifically, they examine high-quality crystals as a function of temperature and applied strain, where the shear modulus reaches a plateau and dissipation becomes close to zero; both quantities are reported to be independent of stress and strain, implying a reversible dissipation process and quantum tunneling. In this Comment, we show that these signatures can be explained with a classical model of thermally activated dislocation glide without the need to invoke quantum tunneling or dissipationless motion. Recently, we proposed a dislocation glide model in solid Helium-4 containing the dissipation contribution in the presence of other dislocations with qualitatively similar behavior [Zhou et al., Philos. Mag. Lett. 92 (2012) 608].