Depinning of a superfluid vortex inside a circular defect

In this work we study the process of depinning of a quantum of circulation trapped inside a disk by an applied two-dimensional superflow. We use the G ross-Pitaevskii model to describe the neutral superfluid. The collective co ordinate dynamics is derived directly from the condensate equation of motio n, the nonlinear Schrodinger equation, and it is used to obtain an expressi on for the critical velocity as a function of the defect radius. This expre ssion is compared with a numerical result obtained from the time-independen t nonlinear Schrodinger equation. Below the critical velocity, we obtain th e dependence of the semiclassical nucleation rate with the how velocity at infinity. above the critical velocity, the classical vortex depinning is il lustrated with a numerical simulation of the time-dependent nonlinear Schro dinger equation.