3He on preplated graphite

TL;DR

Using diffusion Monte Carlo simulations, this study maps the phase diagram of helium-3 on preplated graphite, revealing a stable liquid phase and multiple phase transitions, differing from helium-3 on clean graphite.

Contribution

First comprehensive quantum Monte Carlo analysis of $^3$He on preplated graphite considering substrate atom mobility, predicting new phase behavior and transitions.

Findings

Ground state is a liquid with density 0.007 Å$^{-2}$

Predicted a first-order transition to a 7/12 phase

Identified a transition to an incommensurate triangular phase

Abstract

By using the diffusion Monte Carlo method, we obtained the full phase diagram of $^3$He on top of graphite preplated with a solid layer of $^4$He. All the $^4$He atoms of the substrate were explicitly considered and allowed to move during the simulation. We found that the ground state is a liquid of density 0.007 $\pm$ 0.001 \AA$^{-2}$, in good agreement with available experimental data. This is significantly different from the case of $^3$He on clean graphite, in which both theory and experiment agree on the existence of a gas-liquid transition at low densities. Upon an increase in $^3$He density, we predict a first-order phase transition between a dense liquid and a registered 7/12 phase, the 4/7 phase being found metastable in our calculations. At larger second-layer densities, a final transition is produced to an incommensurate triangular phase.