Thermal Conductivity in a Pure Type II Superconductor near the Upper Critical Field

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Abstract
The thermal conductivity, K , of a pure Nb (RRR=1900) has been studied as a function of longitudinal and transverse magnetic field between 1.8°K and the transition temperature (9.2°K). The thermal conductivity shows a deep minimum just above H c 1 and increases with infinite slope in the gapless region near H c 2 like Δ K / K n = C ( H c 2 - H ) 1/2 in good agreement with the Maki theory for both longitudinal and transverse field configurations. The temperature dependence of the coefficient C is compared with numerically calculated one from the revised Maki theory which includes both the impurity scattering and the phonon scattering, and a fairly good agreement is found between them, when density of states is assumed to be 1.6×10 33 states/cm 3 erg.