4He on a single graphene sheet

The phase diagram of the first layer of ${}^4$He adsorbed on a single graphene sheet has been calculated by a series of diffusion Monte Carlo calculations including corrugation effects. As the number of C-He interactions is reduced with respect to graphite the binding energy of ${}^4$He atoms to graphene is approximately 13.4 K/He atom smaller. Our results indicate that the phase diagram is qualitatively similar to that of helium on top of graphite. A two-dimensional liquid film on graphene is predicted to be metastable with respect to the commensurate solid but the difference in energy between both phases is very small, opening the possibility of such a liquid film to be experimentally observed.