Thermal conductivity of superconducting alloy films in a perpendicular magnetic field
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.
thermal conductivity, superconducting alloy films, perpendicular magnetic field, quench-condensed films
University of Illinois - Urbana-Champaign
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