On the stability of small vacancy clusters in solid 4He

Abstract

We study numerically properties of multiple vacancies in solid 4He at zero temperature. Up to four vacancies were introduced into the solid through incommensuration between the number of available lattice sites and the actual number of atoms. Vacancy-vacancy correlation function increases at very short distances indicating effective vacancy attraction between vacancies located on nearby lattice sites. The decay of the pair correlation function at large distances puts an upper bound on the absolute value of the binding energy varying from 4 mK at melting density to 150 mK at the highest considered density and no lower bound; either the four-vacancy clusters are unbound, or are bound too weakly for the temperatures of the supersolid experiments.