HOLE DISPERSION AND MAGNETIC CORRELATIONS IN CUPRATES

We present a proper reduction scheme from the three-band Hubbard model of the copper oxygen plane in cuprates to an extended r-J-like model. We find additional hopping amplitudes to nearest and next-nearest nei ghbours. The dispersion of one hole is studied by a variational ansatz which agrees well with the exact diagonalization method. The modifica tions due to the additional hopping integrals may explain the deviatio ns from the pure t-J model dispersion which were found recently in the insulating compound Sr2Cu2O2Cl2. We simulate the doping dependence of the dispersion by a frustration term in the Hamiltonian. That influen ces the spin-correlations and also the dispersion changes. We find a t ransition from a dispersion with an isotropic minimum at (pi/2, pi/2) in the undoped case to a dispersion with an extended saddle point at ( pi, 0) similar to the dispersion in doped cuprates.