Novel substrates for Helium adsorption: Graphane and Graphene-Fluoride

TL;DR

This study investigates helium films on novel substrates graphene-fluoride and graphane, revealing unique adsorption potentials, larger effective masses, and superfluid ground states, expanding understanding of helium adsorption behaviors.

Contribution

It introduces the first analysis of helium adsorption on GF and GH substrates, highlighting differences in potential energy, band structure, and superfluidity compared to graphene.

Findings

He on GF has a larger effective mass and higher adsorption energy than on graphite.

Monolayer 4He on GF and GH is superfluid with about 10% Bose-Einstein condensate fraction.

Ordered commensurate states are unstable on GF and GH, unlike on graphite.

Abstract

The discovery of fullerenes has stimulated extensive exploration of the resulting behavior of adsorbed films. Our study addresses the planar substrates graphene-fluoride (GF) and graphane (GH) in comparison to graphene. We present initial results concerning the potential energy, energy bands and low density behavior of 4He and 3He films on such different surfaces. For example, while graphene presents an adsorption potential that is qualitatively similar to that on graphite, GF and GH yield potentials with different symmetry, a number of adsorption sites double that on graphene/graphite and a larger corrugation for the adatom. In the case of GF, the lowest energy band width is similar to that on graphite but the He atom has a significantly larger effective mass and the adsorption energy is about three time that on graphite. Implications concerning the monolayer phase diagram of 4He are explored with the exact path integral ground state method. A commensurate ordered state similar to the sqrt{3} x sqrt{3} R30^o state on graphite is found the be unstable both on GF and on GH. The ground states of submonolayer 4He on both GF and GH are superfluids with a Bose Einstein condensate fraction of about 10%.