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, cons equently, of delta in doped superconductors such as the cuprates. A ge neral equation relating the isotope coefficients of T-c and of delta i s presented for London superconductors. We further show that the prese nce of magnetic impurities or a proximity contact also lead to an isot opic dependence of delta; the isotope coefficient turns out to be temp erature dependent, beta(T), in these cases. The existence of the isoto pe effect for the penetration depth is predicted for conventional as w ell as for high-temperature superconductors. Various experiments are p roposed and/or discussed. [S0163-1829(98)03617-0].