Effect of strong electron correlations on the electron-phonon coupling in high Tc superconductors

Abstract It is shown that the strong electron-electron repulsion on copper suppresses the coupling of phonons to the copper-oxygen charge fluctuation for large charge transfer gap, in contrast to the coupling to the intracell oxygen-oxygen charge fluctuation, which remains undiminished. In addition, when the Fermi level approaches the van Hove singularity on doping the lattice fluctuation which couple to the oxygen-oxygen charge fluctuation is enhanced, irrespective of the value of the charge transfer gap. The relation with experimental observations is discussed.