Isotope effect on the electron band structure of doped insulators

Applying a continuous-time quantum Monte Carlo algorithm we calculate the exact coherent band dispersion and the density of states of a two-dimensional lattice polaron in the region of parameters where any approximation might fail. We find an isotope effect on the band structure, which is different for different wave vectors of the Brillouin zone and depends on the radius and strength of the electron-phonon interaction. An isotope effect on the electron spectral function is also discussed.