Off-diagonal long-range order in solid 4He

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