Thermally activated hopping of a single Abrikosov vortex

Thermally activated hopping of a single Abrikosov vortex has been investigated for a thin Pb film that was decorated with an artificial pinning structure. To determine the location of the vortex, the Pb film is fabricated to be one electrode of a cross-strip superconductor/normal-metal/insulator/superconductor (SNIS') Josephson junction. Distortions in the Fraunhofer pattern specify the vortex location. As the temperature is raised toward Tc, the vortex depins from the artificial pinning site and reproducibly moves through the same sequence of other pinning sites before it leaves the junction area of the Pb film. The first thermal depinning occurs when the order parameter of the bulk superconductor is about 20% of the T=0 value. The trajectory is not random.