Superfluidity in H-2 films

Path integral Monte Carlo calculations were used to study a 2D system of H-2 molecules. The ground state on a flat substrate is a triangular lattice, a localized solid. We find that the introduction of some weakly attractive impurities (specifically alkali metal atoms) in the right concentration (similar to 0.01 Angstrom(-2)) stabilizes a liquid hydrogen phase of concentration 0.04 Angstrom(-2) which undergoes a Kosterlitz-Thouless superfluid transition below approximately 1.2 K.