Imaging vortices in superconducting weakly coupled arrays

Wistrom, Mark

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https://hdl.handle.net/2142/31039 Copy

Description

Title

Imaging vortices in superconducting weakly coupled arrays

Author(s)

Wistrom, Mark

Issue Date

2012-05-22T00:23:44Z

Director of Research (if dissertation) or Advisor (if thesis)

Van Harlingen, Dale J.

Doctoral Committee Chair(s)

Mason, Nadya

Committee Member(s)

• Van Harlingen, Dale J.
• Ryu, Shinsei
• Clegg, Robert M.

Department of Study

Physics

Discipline

Physics

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(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.

Graduation Semester

2012-05

Permalink

http://hdl.handle.net/2142/31039

Copyright and License Information

Copyright 2012 Mark Wistrom

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