Electron-lattice interaction in cuprates: Effect of electron correlation

Strong electron-phonon coupling in the cuprates enhanced by electron correlation is suggested by exact diagonalization of a two-band Peierls-Hubbard Hamiltonian in one dimension. To describe the cuprates the band filling was chosen to be about 3/4, and the effect of changing the copper on-site repulsion and the charge density was examined. The zone-boundary longitudinal optical phonon modes were found to couple very strongly to holes as a result of charge transfer and changes in the local spin correlation induced by deformation. In particular the oxygen mode was found to soften significantly with doping, in agreement with the experimental observation. These results suggest strong synergetic effects of spin-charge-lattice coupling in this system. Implications of these effects to the superconductivity of the cuprates are discussed.