Interaction Energies of Helium Atoms Adsorbed on Graphene

We use density functional theory (DFT) calculations to characterize the interaction energy of helium atoms adsorbed on a graphene substrate. Two-dimensional graphene provides an exciting platform to study the formation of exotic helium phases such as superfluids or supersolids, since quantum phase transitions between such phases can be induced by modifying the lattice properties. For example, graphene’s lattice spacing, and by extension the van der Waals distance for a pair of adsorbed helium atoms, can be controlled through mechanical strain. We characterize the He-He interaction energies for atoms adsorbed on a periodic graphene sheet at nearest-neighbor lattice sites under various strain conditions. We show that strain can effectively tune the He-He interaction energy and describe our results within the context of an effective extended Bose-Hubbard (t-V-V’) model.