Off-Diagonal Long-Range Order in Solid 4He

TL;DR

This study uses Path Integral Monte Carlo to investigate off-diagonal long-range order in solid helium-4, finding no evidence of Bose-Einstein condensation in a perfect crystal at melting density, suggesting correlations suppress BEC.

Contribution

First to use PIMC to calculate ODLRO in solid 4He, showing that perfect crystals lack BEC due to correlation effects.

Findings

No ODLRO found in perfect solid 4He at melting density

Correlations suppress vacancies and BEC in the wave function

Results challenge the interpretation of supersolidity in perfect crystals

Abstract

Measurements of the moment of inertia by Kim and Chan have found that solid 4He acts like a supersolid at low temperatures. To understand the order in solid 4He, we have used Path Integral Monte Carlo to calculate the off-diagonal long range order (ODLRO) (equivalent to Bose-Einstein condensation, BEC). We do not find ODLRO in a perfect hcp crystal at the melting density. We discuss these results in relation to proposed quantum solid trial functions. We conclude that the solid 4He wave function has correlations which suppress both vacancies and BEC.