Thermal conductivity of tantalum and niobium below 1 °K

Abstract

Abstract The thermal conductivity, Ks, of superconductive tantalum and niobium has been measured between 0.2 and 1.2 °K, and for one niobium specimen between 0.2 and 4.2 °K. Large maxima in Ks occur in all three cases at ~ 0.2TC and Ks has been analyzed into its electronic and lattice components Kes and Kgs. Agreement between experiment and the B.C.S. theory is good for tantalum between T = 0.5TC and T = TC, where Kgs is small. Below 0.5TC conduction by phonons becomes appreciable. From the curves of Kgs against T the width of the energy gap at 0 °K has been deduced, giving (2Є0 =) 3.8 ± 0.2kTC for tantalum and (2Є0 =) 3.5 ± 0.2kTC for niobium.