Heat-capacity studies of (3)He in (3)He-(4)He mixture films and the coverage dependence of the two-dimensional (3)He Landau Fermi-liquid parameters

Liquid and Solid Phases of ^{3}He on Graphite

Recent heat-capacity experiments show quite unambiguously the existence of a liquid ^{3}He phase adsorbed on graphite. This liquid is stable at an extremely low density, possibly one of the lowest found in nature. Previous theoretical calculations of the same system, and in strictly two dimensions, agree with the result that this liquid phase is not stable and the system is in the gas phase. We calculated the phase diagram of normal ^{3}He adsorbed on graphite at T=0 using quantum Monte Carlo methods. Considering a fully corrugated substrate, we observe that at densities lower than 0.006  Å^{-2} the system is a very dilute gas that, at that density, is in equilibrium with a liquid of density 0.014  Å^{-2}. Our prediction matches very well the recent experimental findings on the same system. On the contrary, when a flat substrate is considered, no gas-liquid coexistence is found, in agreement with previous calculations. We also report results on the different solid structures, and on the corresponding phase transitions that appear at higher densities.

LOWEST-ORDER CONSTRAINED VARIATIONAL CALCULATIONS FOR TWO-DIMENSIONAL LIQUID 3He

We have used the lowest-order constrained variational (LOCV) method based on the cluster expansion of the energy functional to calculate some ground state properties of two-dimensional liquid 3 He at zero temperature employing the Lennard-Jones and Aziz pair potentials. We have seen that the total energy increases by increasing density. It is shown that the two-dimensional liquid 3 He system has no self-bound state.

Zero-temperature equation of state of two-dimensional 3He

The equation of state of two-dimensional 3He at zero temperature has been calculated using the diffusion Monte Carlo method. By means of a combination of the fixed-node and released-node techniques, it is shown that backflow correlations provide a very accurate equation of state. The results prove unambiguously the non-self-bound character of two-dimensional 3He due to its Fermi statistics. We present solid evidence that the gas phase, predicted for the two-dimensional system, can be extrapolated to the case of 3He adsorbed on a strong substrate such as graphite.

Condensation of 3He and reentrant superfluidity in submonolayer 3He- 4He mixture films on H2

We have studied the effect of 3He on the superfluid response of submonolayer 4He films adsorbed on H2. In a limited range of 4He coverage, the introduction of 3He brings forth sequentially the normal, superfluid, and the normal phase again. This novel behavior is very likely the consequence of the condensation of the 3He atoms confined near the free surface of the superfluid 4He film into a self-bound 2D liquid.