A microscopic description of vacancies in solid 4He

TL;DR

This paper uses quantum Monte Carlo methods to analyze how vacancies affect the properties of solid 4He, revealing significant changes at a specific temperature and insights into vacancy behavior and elastic properties.

Contribution

It provides a microscopic quantum description of vacancies in solid 4He, identifying an onset temperature for property changes and vacancy delocalization.

Findings

Vacancies cause significant property changes in solid 4He.

An onset temperature marks the transition to delocalized vacancies.

Vacancies influence the elastic properties at zero temperature.

Abstract

The changes that vacancies produce in the properties of hcp solid 4He are studied by means of quantum Monte Carlo methods. Our results show that the introduction of vacancies produces significant changes in the behavior of solid 4He, even when the vacancy concentration is very small. We show that there is an onset temperature where the properties of incommensurate 4He change significantly. Below this temperature, we observe the emergence of off-diagonal long range order and a complete spatial delocalization of the vacancies. This temperature is quite close to the temperature where non-classical rotational inertia has been experimentally observed. Finally, we report results on the influence of vacancies in the elastic properties of hcp 4He at zero temperature.