Pinning of a single Abrikosov vortex in superconducting Nb thin films using artificially induced pinning sites

Abstract

Artificial structures were intentionally introduced into Nb films in order to study the interaction of a single Abrikosov vortex with pinning sites caused by these known defects. A vortex trapped on one of these structures or defects can be induced to move either by thermal depinning or by pushing on the vortex with a transport current in one of the films. The resulting motion, in turn, can be followed by observing the changes in the Fraunhofer-like interference pattern of a cross-strip Josephson junction having the thin film as one leg of the junction. Artificial pinning sites were successfully created by depositing Fe balls on the surface of a previously characterized thin film. Attempts to create artificial pinning sites by depressing the order parameter with a thin strip of Au on the surface of the Nb were not successful. There was no correlation between the location of trapped vortices and the location of the Au line. In a separate measurement, Lorentz-force-depinning studies for several intrinsic pinning sites in the thin film show that a transport current in the top film will depin a vortex in the top film with about one-tenth the current needed in the bottom film to depin the same vortex.

Source-reported materials — not catalogue approval

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