Thermal and structural properties of topological defects in solid Helium-4: Strain induced martensitic transformation from hcp to fc orthorhombic lattice

TL;DR

This study investigates how topological defects in solid Helium-4 influence its thermal and structural properties, revealing dislocation-dependent activation energies and a potential phase transition from hcp to orthorhombic structure under stress.

Contribution

It provides new insights into defect-induced modifications of solid Helium-4's behavior and suggests a possible stress-induced phase transition not previously characterized.

Findings

Dislocation type strongly affects activation energy (1K to 20K).

Annihilation of jog-antijog pairs can induce orthorhombic regions.

Solid Helium-4 may undergo a displacive transition under uniaxial stress.

Abstract

Several experimental studies have reported thermally activated behavior of the mechanical response of solid Helium-4 which does not fit into the model of thermally activated Frenkel pairs in an ideal crystal. The purpose of the present work is to investigate how structural topological defects modify the response. Using quantum Monte Carlo Worm Algorithm, we study temperature dependence of fluctuations of the total number of particles in samples of hcp solid Helium-4 containing several types of dislocations. Such fluctuations can be described by the thermal activation law with the activation energy dependent strongly on the type of the dislocation and the crystal density. The extracted values cover a range from about 1K to 20K. It is also found that annihilation of a jog-antijog pair can produce a local region of the solid characterized by the orthorhombic symmetry. This serendipitous observation suggests that hcp solid Helium-4 can undergo a displacive phase transition into the orthorhombic crystal under uniaxial stress of about 10-15%