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Surface impedance of thin superconducting films

Citation

Mason, Peter V. (1962) Surface impedance of thin superconducting films. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechTHESIS:08032011-113156194

Abstract

Theoretical analysis and experimental measurements have been made of the propagation of electromagnetic waves in a structure consisting of two planar superconductors which are of the order of a penetration depth apart. One superconductor is tantalum and is much thicker than a penetration depth; the other is a vacuum evaporated indium film and may be as thin as a penetration depth.

It is shown that such a structure will propagate waves at a phase velocity less than the speed of light in the medium separating the superconductors, a phenomenon that is the result of an inductive component in the surface impedance of the superconductors. The exact velocity is shown to be a function of the thickness parameters in a manner which depends on the law relating the vector potential and the supercurrent in the indium.

Experimental measurements indicate that the relationship between vector potential and current in the vacuum evaporated indium is characterized by a coherence distance which is considerably smaller than that found for pure metals by the measurements of Pippard and the theory of Bardeen, Cooper and Schrieffer.

The penetration depth at zero temperature is deduced from dependence of phase velocity on the thicknesses of the indium and dielectric. For indium λ is found to be 650 ± 75Å, in good agreement with Lock's value of 640° and Toxen's range from 625 to 725Å. For tantalum λ is found to be 500 ± 175Å. This is believed to be the first measurement. The value of λ for indium is also deduced from the dependence of phase velocity on temperature. It is found to be 704 ± 120Å.

Surface resistance of the two superconductors is found to increase ω^2, in good agreement with theory, and to depend on temperature according to an empirical law proposed by Pippard.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Electrical Engineering
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Electrical Engineering
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Gould, Roy Walter (advisor)
  • Mead, Carver (co-advisor)
Thesis Committee:
  • Unknown, Unknown
Defense Date:1 January 1962
Record Number:CaltechTHESIS:08032011-113156194
Persistent URL:http://resolver.caltech.edu/CaltechTHESIS:08032011-113156194
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:6569
Collection:CaltechTHESIS
Deposited By: Tony Diaz
Deposited On:24 Aug 2011 17:10
Last Modified:26 Dec 2012 04:38

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