Quantum Films Adsorbed on Graphite: Third and Fourth Helium Layers
  Using a path-integral Monte Carlo method for simulating superfluid quantum films, we investigate helium layers adsorbed on a substrate consisting of graphite plus two solid helium layers. Our results for the promotion densities and the dependence of the superfluid density on coverage are in agreement with experiment. We can also explain certain features of the measured heat capacity as a function of temperature and coverage. 
Marlon Pierce and Efstratios Manousakis