Structure of metastable 2D liquid helium

TL;DR

This paper reports diffusion Monte Carlo simulations revealing a metastable, superfluid, hexatic phase in 2D helium with anisotropic properties, suggesting a two-stage phase transition from superfluid to crystal.

Contribution

It introduces a new metastable hexatic superfluid phase in 2D helium and details its properties and implications for phase transitions.

Findings

Existence of a metastable, superfluid, hexatic phase in 2D helium.

The phase exhibits finite condensate fraction and anisotropic order.

Phase transition occurs in two stages: superfluid to hexatic, then to crystal.

Abstract

We present diffusion Monte Carlo (DMC) results on a new metastable, superfluid phase above the crystal ground state in two-dimensional 4He at densities > 0.065 1/A^2. The state is anisotropic with hexatic orbital order. This implies that the liquid--solid phase transition has two stages: A second order phase transition from the isotropic superfluid to the hexatic superfluid, followed by a first order transition that localizes atoms into the triangular crystal order. This metastable hexatic phase has finite condensate fraction and it provides a natural explanation for the superflow in the supersolid grain boundaries.