Structure of metastable 2D liquid helium

¹  Department of Physics, University of Jyväskylä - P.O. Box 35, FIN-40014, Finland, EU
²  Department of Physical Sciences, University of Oulu - P.O. Box 3000, FIN-90014, Finland, EU

Received: 15 July 2008
Accepted: 3 October 2008

Abstract

We present diffusion Monte Carlo (DMC) results on a novel, superfluid phase in two-dimensional ⁴He at densities higher than 0.065 Å^-2, which is very close to the freezing density. The new phase has anisotropic, hexatic orbital order, but the single-particle density remains constant. By increasing density the hexatic superfluid forms a metastable state, which lies above the crystal ground state in energy. This implies that the liquid-solid phase transition takes place in 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.