The giant plasticity of a quantum crystal

TL;DR

This paper reveals that helium-4 crystals exhibit a giant, anisotropic, and reversible plasticity at zero temperature due to dislocation motion, which is suppressed by impurities and thermal phonons.

Contribution

It demonstrates the existence of giant, reversible plasticity in helium-4 crystals at zero temperature, driven by dislocation glide along basal planes.

Findings

Helium-4 crystals show nearly zero shear resistance in specific directions.

Impurities and thermal phonons suppress the observed plasticity.

Plasticity is anisotropic and reversible in pure helium-4 crystals.

Abstract

When submitted to large stresses at high temperature, usual crystals may irreversibly deform. This phenomenon is known as plasticity and it is due to the motion of crystal defects such as dislocations. We have discovered that, in the absence of impurities and in the zero temperature limit, helium 4 crystals present a giant plasticity that is anisotropic and reversible. Direct measurements on oriented single crystals show that their resistance to shear nearly vanishes in one particular direction because dislocations glide freely parallel to the basal planes of the hexagonal structure. This plasticity disappears as soon as traces of helium 3 impurities bind to the dislocations or if their motion is damped by collisions with thermal phonons.