Low-density phases of $^3$He monolayers adsorbed on graphite

TL;DR

Quantum Monte Carlo simulations reveal a low-density gas-liquid phase transition in a $^3$He monolayer on graphite, challenging previous assumptions about its phase behavior at ultra-low densities.

Contribution

This study provides the first unbiased quantum Monte Carlo analysis of $^3$He monolayers on graphite, including realistic interactions and substrate effects, identifying a gas-liquid transition at very low densities.

Findings

Gas-liquid phase transition at ~0.01 Å$^{-2}$ density.

Ground state energy calculations support the transition.

Sensitivity of the phase boundary to model details.

Abstract

Quantum Monte Carlo simulations at zero temperature of a $^3$He monolayer adsorbed on graphite, either clean or preplated with $^4$He, unexpectedly point to a gas-liquid phase transition at a very low areal density of the order of 0.01\AA$^{-2}$. This result stems from an essentially unbiased calculation of the ground state energy for an infinite, defect-free substrate which interacts with He atoms via a realistic potential, whereas the interaction between two He atoms includes two- and three-body terms. The sensitivity of the gas-liquid coexistence region on the model Hamiltonian employed is discussed.