Theory of quantum Bose crystals
Abstract
An attempt is made to explain the recently observed unique plastic properties of parahydrogen: flow of crystals in a gravitational field and superplasticity—fluid-like flow under a load. A detailed microscopic study of a Bose crystal with a small number of zero vacancions is carried out. The wave function of the ground state of the crystal is found; an order parameter is introduced for the condensate fraction of the vacancions; and an equation describing slow changes in the order parameter in space and time is derived. The conditions under which vacancies can appear only near the surface of the crystal are determined. In the situation when the surface layer becomes superfluid, the density of quantum vortices accompanying the flow of transport current along the layer is calculated. The mass flowing along the surface of the crystal in the gravitational field is found.