Isotopic shifts in a polaronic system

The effect of isotopic substitution in a model polaronic system is presented. We use a three-site many body electron-phonon model which includes electronic correlations and electron-phonon interactions, showing the presence of polaron tuneling for intermediate and strong couplings. The isotopic substitution changes the dynamics of polaron tuneling. Additionally in the intermediate electron-phonon coupling regime, relevant for high-T_c superconductors, a change in the local structure is predicted. In this regime, the isotopic shift of phonon excitations is consistent with results of optical measurements of c-axis phonons in YBa₂Cu₃O₇.