Bose Einstein Condensation of incommensurate solid 4He

TL;DR

This paper investigates whether solid 4He has an incommensurate ground state with vacancies and finds evidence of vacancy-induced Bose-Einstein condensation, suggesting that bulk solid 4He could be a supersolid at low temperatures.

Contribution

It provides the first computation of the one-body density matrix in incommensurate solid 4He using the Shadow Path Integral Ground State method, revealing vacancy-induced BEC.

Findings

Vacancy concentration of about 0.23 atoms per vacancy at 54 bar

Evidence of Bose-Einstein condensation induced by vacancies

Implication that bulk solid 4He is a supersolid at low temperatures

Abstract

It is pointed out that simulation computation of energy performed so far cannot be used to decide if the ground state of solid 4He has the number of lattice sites equal to the number of atoms (commensurate state) or if it is different (incommensurate state). The best variational wave function, a shadow wave function, gives an incommensurate state but the equilibrium concentration of vacancies remains to be determined. In order to investigate the presence of a supersolid phase we have computed the one--body density matrix in solid 4He for the incommensurate state by means of the exact Shadow Path Integral Ground State projector method. We find a vacancy induced Bose Einstein condensation of about 0.23 atoms per vacancy at a pressure of 54 bar. This means that bulk solid 4He is supersolid at low enough temperature if the exact ground state is incommensurate.