Quantum Monte Carlo simulation of overpressurized liquid 4He

TL;DR

This paper uses diffusion Monte Carlo simulations to study superfluid helium-4 at zero temperature under high pressure, revealing how key properties evolve in the overpressurized, metastable phase.

Contribution

It provides the first detailed quantum Monte Carlo analysis of superfluid helium-4 beyond freezing pressure, including the equation of state and excitation properties in the overpressurized regime.

Findings

Condensate fraction decreases but remains finite at high pressures.

Roton energy decreases with pressure but does not vanish.

Results agree with recent experimental data in the overpressurized phase.

Abstract

A diffusion Monte Carlo simulation of superfluid $^4$He at zero temperature and pressures up to 275 bar is presented. Increasing the pressure beyond freezing ($\sim$ 25 bar), the liquid enters the overpressurized phase in a metastable state. In this regime, we report results of the equation of state and the pressure dependence of the static structure factor, the condensate fraction, and the excited-state energy corresponding to the roton. Along this large pressure range, both the condensate fraction and the roton energy decrease but do not become zero. The roton energies obtained are compared with recent experimental data in the overpressurized regime.