Theory for supersolid He4: Vacancy condensation facilitated by a low-energy bound state of a vacancy and an interstitial

Abstract

Although both vacancies and interstitials have relatively high activation energies in the normal solid, we propose that a lower energy bound state of a vacancy and an interstitial may facilitate vacancy condensation to give supersolidity in He4. We use a phenomenological two-band boson lattice model to demonstrate this new mechanism and discuss the possible relevance to the recently observed superfluidlike, nonclassical rotational inertial experiments of Kim and Chan in solid He4. Some of our results may also be applicable to trapped bosons in optical lattices. © 2005 The American Physical Society.