Dynamical Mechanisms of Vortex Pinning in Superfluid Thin Films

We characterize the mechanisms of vortex pinning in a superfluid thin film described by the twodimensional Gross-Pitaevskii equation. We consider a vortex scattering experiment whereby a single vortex in a superfluid flow interacts with a circular, uniform pinning potential. By an analogy with linear dielectrics, we develop an analytical hydrodynamic approximation that predicts vortex trajectories, the vortex fixed point and the unpinning velocity. We then solve the Gross-Pitaevskii equation to validate this model, and build a phase portrait of vortex pinning. We identify two different dynamical pinning mechanisms marked by distinctive phonon emission signatures: one enabled by acoustic radiation and another mediated by vortex dipoles nucleated within the pin. Relative to obstacle size, we find that pinning potentials on the order of the healing length are more effective for vortex capture. Our results could be useful in mitigating the negative effects of drag due to vortices in superfluid channels, in analogy to maximizing supercurrents in type-II superconductors.

Automated summary

This study characterizes vortex pinning mechanisms in a superfluid thin film described by the two-dimensional Gross-Pitaevskii equation. Two different dynamical pinning mechanisms are identified, and it is found that pinning potentials on the order of the healing length are more effective in capturing vortices.