Vortex configurations in a freely rotating superfluid drop

The equilibrium configurations of a single vortex in a freely rotating superfluid drop have been determined. The potential barrier to vortex nucleation has also been examined. A freely rotating drop is constrained to rotate at a fixed angular momentum, as opposed to fluid in a rotating vessel, where the vessel is usually constrained to rotate at fixed angular velocity. Vortex configurations that minimize the free energy have been found for a range of angular momenta. These configurations are not necessarily on the axis of rotation as is the case for a vessel rotating at a constant angular velocity. The nucleation of a vortex is shown to be opposed by a barrier in the free energy. This barrier narrows and decreases in height as the angular momentum of the drop is increased.