Superconductivity and incommensurate spin fluctuations in a generalized t-J model for the cuprates

We consider the slave-fermion Schwinger-boson decomposition of an effective model obtained through a systematic low-energy reduction of the three-band Hubbard Hamiltonian. The model includes a three-site term t '' similar to that obtained in the large-U limit of the Hubbard model but of opposite sign for realistic or large O-O hopping. For parameters close to the most realistic ones for the cuprates, the mean-field solution exhibits d + s superconductivity (predominantly d(x2-y2)) With a dependence on doping x very similar to the experimentally observed. We also obtained incommensurate peaks at wave vectors similar to pi(1, 1 +/- 2x) in the spin structure factor, which also agree with experiment.