The Isotope Effect in Superconductivity. II. Tin and Lead

Abstract

The critical magnetic fields, $H$, of various isotopic mixtures of tin and of lead have been measured as a function of temperature, $T$.For tin, the critical temperature ${T}_{c}$ at zero field, is related to the average mass number, $M$, by the relation ${M}^{0.46}{T}_{c}=\mathrm{const}$. The critical magnetic fields, ${H}_{0}$, at absolute zero are proportional to the critical temperatures. The normalized values of critical field, $\frac{H}{{H}_{0}}$, are the same function of the variable $\frac{T}{{T}_{c}}$ for all the isotopes. An analytic expression for this function giving the best fit to the experimental data is given.The measurements on lead were made in the temperature range 1.6\ifmmode^\circ\else\textdegree\fi{}K to 4.2\ifmmode^\circ\else\textdegree\fi{}K. The data clearly indicate that the isotope effect is present in this superconductor.