Critical Field Curve of Superconducting Mercury

Abstract

The critical field curve of mercury has been precisely measured in a range of reduced temperature, $t=\frac{T}{T_c}$, from 1 to 0.27. The observed $H_c$ values show an appreciable deviation from a parabolic temperature dependence, lying above the parabola which passes through the experimental values of $H_0$ and $T_c$. The general behavior is similar to that previously observed in the case of lead. Values of the temperature coefficient of the normal electronic specific heat, $\gamma$, are derived, but are somewhat uncertain since the $H_c$ data indicate an appreciable entropy contribution from the superconducting electrons at the lowest temperature of measurement. The qualitative behavior of $H_c\mathrm{}\left(T\right)\mathrm{}$ for lead and mercury is in accord with recent infrared measurements which give direct indication that the energy gap value for these elements is anomalously large.