Critical Field Measurements on Superconducting Lead Isotopes

Abstract

The measurement of the isotope effect upon the superconducting critical field of lead has been extended from $T_c$ to 1.28°K, and an accurate critical-field curve for lead is reported for this temperature range. The measured critical-field curve is expanded as a function of $T^2$ and used in calculating the thermodynamic properties of lead. The values for the coefficient of the electronic specific heat in the normal state and for the latent heat of the superconducting transition are in good agreement with calorimetric measurements. The electronic specific heat in the superconducting state does not show an exponential $\frac{1}{T}$ dependence but instead a close resemblance to a $T^4$ dependence below 5°K.