Vortex equilibrium in film flow near a defect

Abstract

A simple model based on numerical simulations in bulk is used to examine the pinning characteristics of vortices in helium films adsorbed in the vicinity of substrate defects. The film profile in the absence of a vortex is first calculated including both the Van der Waals potential of a bump defect and surface tension. The displacement and ultimate de-pinning of a vortex line constrained within the profile is then followed as a function of an imposed superfluid flow. The behavior of the vortices lends insight into recent experimental results sensitive to the presence of pinned vortices and indicates that the relevant pinning sites are atomic in dimension.