Path-integral calculation of the two-dimensional 4He phase diagram

Path-integral Monte Carlo simulations have been used to determine the phase diagram of a two-dimensional He-4 film in a range of temperatures and coverages where it undergoes solidification, superfluidity, and a liquid-gas transition (0.25 K less than or equal to T less than or equal to 1.5 K 0<sigma<0.094 Angstrom(-2)). We determine the phase-transition densities and give the coefficients for a functional form of the free energy in the liquid, solid, and gas phases. The phase diagram is similar to the one determined from experimental measurements of a second layer of helium on graphite.