Theory for supersolid $^4$He

TL;DR

This paper proposes a new mechanism for supersolidity in solid helium-4 involving a bound state of vacancies and interstitials, modeled through a two-band boson lattice approach, potentially explaining recent experimental observations.

Contribution

It introduces a phenomenological two-band boson lattice model to explain supersolidity via vacancy-interstitial bound states in helium-4.

Findings

Bound state of vacancy and interstitial lowers energy barrier

Model explains superfluid-like behavior in solid helium-4

Results may apply to trapped bosons in optical lattices

Abstract

Although both vacancies and interstitial 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 $^{4}$He . We use a phenomenological two-band boson lattice model to demonstrate this new mechanism and discuss the possible relevance to the recently observed superfluid-like, non-classical rotational inertial experiments of Kim and Chan in solid $^{4}$He. Some of our results may also be applicable to trapped bosons in optical lattices.