The Isotope Effect in Superconductivity. II. Tin and Lead

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 Tc at zero field, is related to the average mass number, M, by the relation M0.46Tc=const. The critical magnetic fields, H₀, at absolute zero are proportional to the critical temperatures. The normalized values of critical field, HH₀, are the same function of the variable TTc 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^∘{}K to 4.2^∘{}K. The data clearly indicate that the isotope effect is present in this superconductor.