Thermal conductivity of superconducting alloy films in a perpendicular magnetic field
Willis, Jeffrey Owen
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https://hdl.handle.net/2142/25670
Description
Title
Thermal conductivity of superconducting alloy films in a perpendicular magnetic field
Author(s)
Willis, Jeffrey Owen
Issue Date
1976
Doctoral Committee Chair(s)
Ginsberg, D.M.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
thermal conductivity
superconducting alloy films
perpendicular magnetic field
quench-condensed films
Language
en
Abstract
We have measured the thermal conductivity of superconducting films
of In - Bi alloys in a perpendicular magnetic field. The films were
quench-condensed onto glass substrates held at 77 K, and had thicknesses
ranging from l050 to 4570 A. The ratios of the BCS coherence length to the
electron mean free path for these films were in the range 9 to 10. We made
measurements at several temperatures between 0.3 and 1.0 K for magnetic
fields from zero to above the upper critical field Hc2. We plotted the
thermal conductivity as a function of magnetic field. The resulting curve,
except for some rounding very close to Hc2,was found to be approximately
linear for magnetic fields greater than 60% of Hc2 ' This linear behavior
is in qualitative agreement with the theory of Caro1i and Cyrot for the
electronic thermal conductivity of a dirty superconductor near Hc2. This
theory predicts that the ratio of the slope of the thermal-conductivity
curve to the slope of the magnetization curve at Hc2 is a universal function
of the reduced temperature. We infer the magnetization of our films with
the help of theoretical calculations based on the critical-field values.
The experimental ratios of the slopes are 10 to 30% below the theoretical
values. In attempting to explain this discrepancy, we speculate that K2
varies more rapidly than theory predicts. The same conclusion has been
drawn previously from both similar and different types of experiments.
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