Topological defects and HCP nucleation in BCC helium

Abstract

We propose a new model for the nature of the nucleation of HCP from BCC helium. The dynamic release of shear at the surface of the BCC–HCP phase boundary, sustains the simultaneous nucleation and growth of topological defects in the BCC phase. The topological defects are lines of dynamic shear in the BCC phase. The shear energy gain of this process balances the surface tension, as the growing HCP surface is quickly covered by many defect-loops. We show that this scenario gives better agreement with experiments, which differ with the classical theory of homogeneous nucleation by 6–10 orders of magnitude.