Superfluid and supersolid phases of 4He on the second layer of graphite

TL;DR

This study uses quantum Monte Carlo methods to explore the phase diagram of the second helium layer on graphite, revealing superfluid, supersolid, and stable incommensurate phases, and clarifying the stability of various structures.

Contribution

It provides new computational evidence for superfluid and supersolid phases in 4He on graphite, and clarifies the stability of different crystalline arrangements.

Findings

Evidence of a superfluid phase with hexatic correlations

Identification of a quasi-two-dimensional supersolid at 7/12 registration

The 4/7 commensurate solid is unstable at the studied conditions

Abstract

We revisited the phase diagram of the second layer of 4He on top of graphite using quantum Monte Carlo methods. Our aim was to explore the existence of the novel phases suggested recently in experimental works, and determine their properties and stability limits. We found evidence of a superfluid quantum phase with hexatic correlations, induced by the corrugation of the first Helium layer, and a quasi-two-dimensional supersolid corresponding to a 7/12 registered phase. The 4/7 commensurate solid was found to be unstable, while the triangular incommensurate crystals, stable at large densities, were normal.