Superhexatics

TL;DR

This paper proposes a theoretical model for a new phase of helium-4 films exhibiting both superfluidity and hexatic order, with transitions of the Kosterlitz-Thouless type influenced by each other.

Contribution

It introduces a novel theoretical framework describing a state with simultaneous superfluid and hexatic order in helium films, connecting two types of order and their phase transitions.

Findings

Both superfluid and hexatic transitions are of Kosterlitz-Thouless type.

Superfluid stiffness is affected by the hexatic transition.

Potential relevance to recent helium film experiments.

Abstract

We develop a theory for a novel state of ${}^4$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 of 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.