Phase diagram of second layer of helium adsorbed on graphite
  Using realistic helium-helium and helium-graphite interactions and the path integral Monte Carlo method, we are able to identify the gas, superfluid liquid, commensurate-solid, and incommensurate-solid phases, and the coexistence regions between them, for the second layer of helium on graphite. The phase boundaries and the specific heat that we determine are in good agreement with experiment. The appearance and disappearance of superfluidity with increasing coverage can be explained by the growth of coexistence phases, as was observed by torsional oscillator experiments. 
Marlon Pierce and Efstratios Manousakis