Supersolidity in the second layer of para-H2 adsorbed on graphite

We calculated the phase diagram of the second layer of para-H2 adsorbed on graphite using quantum Monte Carlo methods. The second layer shows an incommensurate triangular crystal structure. By using a symmetric wave function, which makes possible molecule exchanges, we observed that this nearly two-dimensional crystal shows a finite superfluid density around a total density of 0.1650 Å-2. The superfluid fraction of this supersolid phase was found to be small, (0.41±0.05)%, but still experimentally accessible.Postprint (published version