Vortex-loops and solid nucleation in superfluid 4He and 3He

We propose a new model for the nature of the nucleation of solid from the superfluid phases of He-4 and He-3. Unique to the superfluid phases the solid nucleation involves an extremely fast solidification front. We depart from the usual "quasi-static" treatment of solid nucleation by proposing that the nucleation of a solid seed is helped by the simultaneous nucleation of vortex-loops in the superfluid around it. It is the composite entity which is nucleated out of the over-pressurized liquid. This occurs when the local release of pressure creates a velocity field in the superfluid which in turn facilitates the nucleation of vortex-loops. The kinetic energy gain of this process balances the surface tension, as the solid surface is quickly covered by many vortex-loops ("hairy snow-ball"). We show that this scenario gives good agreement with many experiments on heterogeneous nucleation, where the energy barrier is found to differ with the classical theory of homogeneous nucleation by 8 orders of magnitude. We propose several experiments that could show the involvement of vortices with solid nucleation.