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

Direct measurements of the in-plane London penetration depth lambda(L) have recently been performed on high-temperature superconducting copper oxides by a new low-energy muon spin rotation technique. The results show that lambda(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.