Polaronic origin of the isotope effect on the London penetration depth in high-temperature superconducting oxides

Abstract

Direct measurements of the in-plane London penetration depth λ _L have recently been performed on high-temperature superconducting copper oxides by a new low-energy muon spin rotation technique. The results show that λ _L is isotope dependent, evidencing unconventional electron–phonon interactions as its source. The data are interpreted here in terms of polaronic effects on the single-particle energies, which leads to level shifts and exponential band narrowing. Good agreement with the experimental data is obtained.

Acknowledgements

It is a pleasure to acknowledge many helpful discussions with K. A. Müller and H. Keller. We are especially indepted to H. Keller for providing the experimental data prior to publication. R. M. acknowledges support from the Foundation for Polish Science.