H2 superglass on an amorphous carbon substrate

Abstract

The phase diagram of a para-H2 monolayer absorbed on an experimentally synthesized amorphous carbon sheet was calculated using a diffusion Monte Carlo technique. We found that the ground state of that system changed drastically from a perfectly flat substrate to a situation in which the carbon atoms were allowed a certain degree of disorder in the z direction. In the first case, at zero pressure we have a glass of density 0.056 +/- 0.003 angstrom-2 in equilibrium with an incommensurate solid of 0.068 +/- 0.002 angstrom-2. At the equilibrium density, the glass was found to have a tiny, but non-negligible superfluid fraction of less than 1% (0.44 +/- 0.05%). In the z-disordered substrate, we observe a significant enhancement of the superfluid fraction in the glass phase as well as a smaller but not zero value in the incommensurate crystal.