Surface Curvature and Vortex Stability
We examine the stability of a pinned superfluid helium vortex line by measuring its persistence at elevated temperatures. Each vortex terminates at the surface of the container, at either a rounded bump or a conical indentation. We find that pinning with the bump termination is much easier to overcome thermally. This behavior would not be expected from considerations of vortex line tension alone. We take the observations as evidence of an additional contribution to the pinning energetics arising from the interaction of the superfluid order parameter singularity with the curvature of the container's surface. By favoring pinning at points of negative Gaussian curvature, the surface interaction makes the bump a less advantageous pin site.