Ground-state properties and superfluidity of two- and quasi two-dimensional solid 4He

TL;DR

This study uses diffusion Monte Carlo to explore ground-state properties and superfluidity in 2D and quasi-2D solid helium-4, finding negligible superfluidity in pure 2D but finite superfluid density in quasi-2D due to atomic motion.

Contribution

It introduces a new symmetric trial wave function and applies it to study superfluidity in 2D and quasi-2D solid helium-4 using diffusion Monte Carlo.

Findings

Ground-state energy and densities agree with previous Monte Carlo results.

Superfluid fraction is negligible in pure 2D solid helium-4.

Finite superfluid density appears in quasi-2D due to atomic motion.

Abstract

In a recent study we have reported a new type of trial wave function symmetric under the exchange of particles and which is able to describe a supersolid phase. In this work, we use the diffusion Monte Carlo method and this model wave function to study the properties of solid 4He in two- and quasi two-dimensional geometries. In the purely two-dimensional case, we obtain results for the total ground-state energy and freezing and melting densities which are in good agreement with previous exact Monte Carlo calculations performed with a slightly different interatomic potential model. We calculate the value of the zero-temperature superfluid fraction \rho_{s} / \rho of 2D solid 4He and find that it is negligible in all the considered cases, similarly to what is obtained in the perfect (free of defects) three-dimensional crystal using the same computational approach. Interestingly, by allowing the atoms to move locally in the perpendicular direction to the plane where they are confined to zero-point oscillations (quasi two-dimensional crystal) we observe the emergence of a finite superfluid density that coexists with the periodicity of the system.