Interplay between electron-phonon and Coulomb interactions in cuprates

Evidence for strong electron-phonon coupling in high-T-c cuprates is reviewed, with emphasis on the electron and phonon spectral functions. Effects due to the interplay between the Coulomb and electron-phonon interactions are studied. For weakly doped cuprates, the phonon self-energy is strongly reduced due to correlation effects, while there is no corresponding strong reduction for the electron self-energy. Polaron formation is studied, focusing on effects of Coulomb interaction and antiferromagnetic correlations. It is argued that experimental indications of polaron formation in undoped cuprates are due to a strong electron-phonon interaction for these systems.