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Title:Imaging vortices in superconducting weakly coupled arrays
Author(s):Wistrom, Mark
Director of Research:Van Harlingen, Dale J.
Doctoral Committee Chair(s):Mason, Nadya
Doctoral Committee Member(s):Van Harlingen, Dale J.; Ryu, Shinsei; Clegg, Robert M.
Department / Program:Physics
Discipline:Physics
Degree Granting Institution:University of Illinois at Urbana-Champaign
Degree:Ph.D.
Genre:Dissertation
Subject(s):Scanning SQUID Microscope
Superconducting arrays
Abstract:This thesis presents the direct observations of magnetic flux vortices in superconducting weakly coupled arrays. Real space images of vortices were obtained for various values of f, the fractional flux per unit cell in the array, and , the strength of the coupling between the islands of the superconducting array. Images and results were obtained for a single vortex in a triangular array, demonstrating the effect of changing , which increased the penetration depth of the magnetic field of the vortex in the sample. The ground state of a triangular array is measured and discussed as a function of f with emphasis for f = 1/4, 1/3 where there are several degenerate ground states corresponding to different vortex patterns. Annealing the arrays at a particular f is also discussed. In particular, for a square array at f = 1/2, the domain walls are the dominant defects, and they move through the sample as the temperature increases resulting in a single domain. The instrument used to perform the experiments, a Scanning SQUID Microscope (SSM), is discussed. The vortices in the superconducting arrays have weak magnetic fields that change over small length scales, requiring certain techniques for measurement. Also presented are the numerical calculations relating the magnetic field output from the SSM to the underlying phases of the array.
Issue Date:2012-05-22
URI:http://hdl.handle.net/2142/31039
Rights Information:Copyright 2012 Mark Wistrom
Date Available in IDEALS:2012-05-22
Date Deposited:2012-05


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