Isotope Effect in Superconducting Lead

Abstract

The present work is a continuation of earlier measurements of the difference in critical fields of superconducting Pb specimens with various isotopic masses. The isotope samples have been repurified and the low-temperature behavior is now more fully understood. The results near ${T}_{c}$ are consistent with the relation ${T}_{c}=\mathrm{const}\ifmmode\times\else\texttimes\fi{}{M}^{p}$, where $M$ is the average isotopic mass, and yield a value $p=\ensuremath{-}0.478\ifmmode\pm\else\textpm\fi{}0.014$. The measurements at lower temperatures confirm the similarity principle to within approximately 0.1% and indicate that $\ensuremath{\gamma}$, the coefficient in the normal electronic specific heat, is independent of isotopic mass to a similar accuracy.