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-forcedepinning 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.

Optical manipulation of single flux quanta

“…Using expression (2) of the thermal force and taking λ 0 =90 nm and λ 0 / ξ 0 =9 relevant to our niobium film, we deduce a maximal pinning force per vortex unit length F p ∼14 pN μm −1 . This order of magnitude estimate is in accordance with previous determinations based on critical current measurements on similar samples 20 21 22 23 . Finally, the temperature dependence of the pinning force of a strongly bound vortex is displayed in Fig.…”

Static properties of small Josephson tunnel junctions in an oblique magnetic field

“…, where C is the ring mean circumference. The measurement of ∆ requires an external field smaller than the one required for H c ; henceforth, this new parameter also turns out to be a very useful quantity whenever the junction critical field cannot be experimentally determined since it exceeds the irreversible field, i.e., when the Abrikosov vortices first enter into the superconducting films and become pinned in the junction 16 . For our samples the transverse irreversible field was about 5 mT (50 Gauss).…”

Smooth vortex precession in superfluid4He

“…Although in principle superfluid experiments can verify theoretical and computational models of vortex dynamics, few measurements can probe individual vortex behavior. Two exceptions are the observation of a precessing vortex in a Bose-Einstein condensate [6] and diffraction experiments on superconducting vortices [7]. However, these techniques have limitations for dynamical studies, the former because of the condensate lifetime and the latter because of the time for each measurement.…”