Exact-diagonalization study of electron-lattice coupling in the effective two-band t-J model

The effective two-band t-J Hamiltonian for holes in Cu-O planes of cuprates is obtained from the three-band Hubbard Hamiltonian. In this model a doped oxygen hole together with two neighboring copper holes is treated as a composite spin-1/2 three-sites particle. The model is studied by exact diagonalization ina Cu16O32 square cluster. Both binding energy and hole-hole correlation function indicate that two holes bind together for J/t>0.11 and are predominantly located on the next-nearest oxygen sites in the same Cu-O chain. Electron-phonon interaction is studied in the adiabatic phonons approximation. Copper (pi,0) "half-breathing'' mode is shown to couple strongly to doped holes and increase the hole-hole correlation as well as the binding energy. These results are compared with experimental data. [S0163-1829(98)01538-0].