Isotope effect for the penetration depth in superconductors

We show that various factors can lead to an isotopic dependence of the penetration depth delta. Nonadiabaticity (Jahn-Teller crossing) leads to the isotope effect of the charge-carrier concentration n and, consequently, of delta in doped superconductors such as the cuprates. A general equation relating the isotope coefficients of T-c and of delta is presented for London superconductors. We further show that the presence of magnetic impurities or a proximity contact also lead to an isotopic dependence of delta; the isotope coefficient turns out to be temperature dependent, beta(T), in these cases. The existence of the isotope effect for the penetration depth is predicted for conventional as well as for high-temperature superconductors. Various experiments are proposed and/or discussed. [S0163-1829(98)03617-0].