A classical picture of the role of vacancies and interstitials in Helium-4

TL;DR

This study uses classical Monte Carlo simulations to explore how vacancies and interstitials behave in Helium-4, revealing strong binding energies and clustering phenomena that relate to supersolidity.

Contribution

It provides a classical perspective on vacancy and interstitial interactions in Helium-4, highlighting binding energies and dislocation formation relevant to supersolid behavior.

Findings

Strong vacancy binding energy similar to quantum results

Large interstitial binding energy due to dislocation pairing

Clustering of interstitials reduces elastic energy

Abstract

Motivated by experimental hints for supersolidity in Helium-4, we perform Monte Carlo simulations of vacancies and interstitials in a classical two-and three-dimensional Lennard-Jones solid. We confirm a strong binding energy of vacancies which is of the order of Lennard-Jones attraction. This is reminiscent of what has been found for vacancies in Quantum Monte Carlo simulations. In addition, we find a strong attraction and large binding energy of interstitials in two-dimensional simulations. This is mainly due to the formation of a pair of dislocations by clustering interstitials, in which minimizes the elastic deformation energy. We interpret the results in light of the properties of Helium-4.