PHONON-INDUCED PAIRING IN THE 2-DIMENSIONAL HUBBARD-MODEL

We address the problem of electron-phonon interaction in the two dimen sional Hubbard model. The Frohlich canonical transformation has been g eneralized to the case of strongly correlated electrons. The resulting pairing interaction is definitively reduced when compared to the unco rrelated limit. However, among different contributions, the formation of intersite, s-like Cooper pairs is enhanced for small hole concentra tion. We conclude that within the weak coupling theory phonon mediated pairing interactions play a secondary role and can be dominated by ph onon-free mechanisms. This may not be the case for strong electron-pho non coupling.