Theoretical study of H2 in a two-dimensional crystalline matrix

We have carried out extensive path integral Monte Carlo simulations of two-dimensional para-hydrogen (p-H2) embedded in a crystalline matrix of alkali atoms. Our results show that, at low temperatures (∼<5 K), the thermodynamically stable phase of p-H2 is a solid, commensurate with the underlying lattice. A nonzero superfluid signal for p-H2 is observed in simulated systems of very small size (e.g. 13 molecules); however, results for systems of larger sizes are altogether consistent with absence of superfluidity in the thermodynamic limit