Thermal conductivity of superconducting niobium
The magnetic field and temperature dependence of the thermal conductivity of superconducting niobium have been measured in magnetic fields which ranged .. from zero to above the critical fields, and for temperatures which ranged from 0.31 K to above the transition temperature. Measurements were made on a single crystal cylindrical specimen for which R300/R ~ 200. The thermal 4.2:N conductivity in the superconducting state exhibited a maximum near 1.80 K. This maximum has been attributed to enhanced lattice conductivity as the electrons cono dense into the ground state. Below 0.6 K the superconducting state thermal conductivity showed an anomalous 3 departure from the expected T dependence for phonons. The departure has been interpreted in terms of a two energy gap model. Magnetic field measurements with the field parallel to the heat flow showed a deep minimum between H 1 and H at the temperature of the maximum C C2 and at lower temperatures. The experimental results near HC2 have been compared with Maki's prediction that (dKII/dH)CX:(HC2-H)-1/2. Good qualitative agreement was found) but the quantatative results gave a density of states somewhat lower than the values obtained from specific heat measurements.
thermal conductivity, superconducting niobium, magnetic field, single crystals
University of Illinois - Urbana-Champaign
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