Degree Type

Dissertation

Date of Award

1999

Degree Name

Doctor of Philosophy

Department

Physics and Astronomy

First Advisor

D. K. Finnemore

Abstract

Cross-strip superconductor-normal-insulator-superconductor Josephson junctions have been fabricated in order to study the pinning of a single Abrikosov vortex trapped within thin films of Nb. The vortex would be induced to move either by thermal depinning or by pushing on the vortex with a transport current in one of the films. Thermal depinning studies show that the temperature of the initial motion of the vortex is independent of applied fields up to +/-20 mG but the temperature where the vortex exits the junction seems to be about 50 mK lower in +/-20 mG than in zero field. Lorentz force depinning studies show that for a vortex pinned in the top Nb film, there is a large difference between the top and bottom film depinning currents. 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 this vortex. Attempts to create artificial pinning sites by depositing Fe balls on the junction were successful with the vortex being pinned to the site of the Fe ball. Attempts to create an artificial pinning site by depressing the order parameter with a thin strip of Au on the surface of the Nb was not successful. Pinning sites in the Nb were not correlated with the location of the Au lines.

DOI

https://doi.org/10.31274/rtd-180813-13911

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Matthew Joseph Breitwisch

Language

en

Proquest ID

AAI9940183

File Format

application/pdf

File Size

126 pages

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