Heat Capacities of Vanadium and Tantalum in the Normal and Superconducting Phases

The heat capacities of two samples of vanadium and two of tantalum have been measured in the normal and superconducting phases in the temperature interval between 1.7° and 5°K. Below the transition temperature $T_0$, the superconducting heat capacity of both metals could be represented accurately by the relation $C_s=AT+B{T}^2$. In the normal phase the data obeyed the usual relation $C_n=\gamma T+\left(\frac{464}{{\theta }^3}\right)T^3$. From these data $H$ vs $T$ curves were calculated and values of $H_0$, the threshold field at absolute zero, were obtained. For the better vanadium sample the values of the various constants were found to be $T_0=4.89\mathrm{}°$K, $A=-1.97\mathrm{}\times {10}^{-3\mathrm{}}$ cal/mole ${\mathrm{deg}}^2$, $B=1.69\mathrm{}\times {10}^{-3\mathrm{}}$ cal/mole ${\mathrm{deg}}^3$, $\gamma =21.1\mathrm{}\times {10}^{-4\mathrm{}}$ cal/mole ${\mathrm{deg}}^2$, $\Theta =273\mathrm{}°$K, and $H_0=1340\mathrm{}$ oersteds; for the better tantalum sample $T_0=4.38\mathrm{}°$K, $A=-1.45\mathrm{}\times {10}^{-3\mathrm{}}$ cal/mole ${\mathrm{deg}}^2$, $B=1.33\mathrm{}\times {10}^{-3\mathrm{}}$ cal/mole ${\mathrm{deg}}^3$, $\gamma =13.0\mathrm{}\times {10}^{-4\mathrm{}}$ cal/mole ${\mathrm{deg}}^2$, $\Theta =231\mathrm{}°$K, and $H_0=860\mathrm{}$ gauss. The measured heat capacities were compared with the predictions of the Koppe theory and the $\alpha$ model.