Hexatically ordered superfluids

Abstract

We develop a theory for a novel state of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ films that possesses off-diagonal order (as in the superfluid state) as well as hexatic or bond orientational order. Within our description, both the hexatic and superfluid transitions are still on the Kosterlitz-Thouless type, but the superfluid stiffness is sensitive to the hexatic transition. We briefly discuss the possible relevance of this work to recent experiments on submonolayer helium films.