Pressure Effect on Superconducting Lead

Techniques are described for measuring the effect of hydrostatic pressure on the critical field, $H_c$, of superconducting Pb. Pressures up to 650 atm were applied using solid helium as the pressure fluid. Observations were made from about 7 to 1°K, and values of $\frac{d{H}_0}{\mathrm{dP}}$, $\frac{d{T}_c}{\mathrm{dP}}$, and the temperature variation of ${\left(\frac{\partial H_c}{\mathrm{dP}}\right)}_T$ are reported. From these data the value of $\left(\frac{1}{{\gamma }^{*}}\right)\left(\frac{d{\gamma }^{*}}{\mathrm{dP}}\right)$ is deduced, where ${\gamma }^{*}$ is the temperature coefficient per unit volume of the normal electronic specific heat. The observed data are accurately represented over the full range of measurement by the equation $H_c(P, T)=H_0\mathrm{}\left(P\right)f\left(t\right)\mathrm{}$ where $t=\frac{T}{T_c}$ and $f\left(t\right)\mathrm{}$ is independent of pressure. The "similarity principle" requirement, $\frac{H_0\mathrm{}\left(P\right)\mathrm{}}{T_c\mathrm{}\left(P\right)\mathrm{}}=\mathrm{const}$, is shown to be invalid for Pb. The results provide the basis for a discussion of the pressure effects on the net interaction potential, $V$, of the Bardeen, Cooper, Schrieffer theory and the density of electronic states near the Fermi surface.