Vacancy-induced transitions in hcp ³He

Abstract

It is known from the work of Nagaoka that in hcp or fcc ³He a ferromagnetic alignment of nuclear spins does not give the lowest vacancy energy. We show that an ordered spin structure has a lower vacancy energy than either random or ferromagnetic structures. We study the possibility of vacancies inducing a transition to this spin structure, and of vacancies forming polarons. The latter is found to be more likely, and we estimate the fraction of vacancies forming polarons as a function of temperature. We briefly comment on the case of a vacancy in crystals of ⁴He with ³He impurity.