Abstract
We investigate the isotope effect on the London penetration depth of a superconductor which measures , the ratio of superfluid density to effective mass. We use a simplified model of electrons weakly coupled to a single phonon frequency , but assume that the energy gap does not have any isotope effect. Nevertheless, we find an isotope effect for which is significant if is sufficiently large that it becomes comparable to , a regime of interest to high- cuprate superconductors and possibly other families of unconventional superconductors with relatively high . Our model is too simple to describe the cuprates and it gives the wrong sign of the isotope effect when compared with experiment, but it is a proof of principle that the isotope effect exists for in materials where the pairing gap and are not of phonon origin and have no isotope effect.
- Received 23 September 2010
DOI:https://doi.org/10.1103/PhysRevB.83.024506
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