3-BAND T-J MODEL - A SYSTEMATIC LARGE-N ANALYSIS

We investigate the physical properties of a three-band generalized t-J model within a systematic large-N slave boson approach allowing for d imer, flux, and uniform magnetic order. The mean-field (N = infinity) phase diagrams are characterized by the presence of phase separation, resulting from the competition of kinetic and magnetic energy, which i s not spoiled by the inclusion of a direct oxygen-oxygen hybridization term, or of a copper-oxygen short-range Coulombic interaction term, a nd could be of some relevance in the description of the high-temperatu re superconducting cuprates. However, such a phase separation takes pl ace between a magnetic dimer insulating phase and a metallic phase wit h flux order, which is not experimentally observed. The question of th e stability of such an exotic phase is addressed in detail showing tha t the stability region of the flux phase can be greatly reduced especi ally by removing the nesting in the uniform Fermi-liquid phase and by the effects of the temperature. This scenario leaves open the possibil ity of an electronic origin of the phase separation observed in the cu prates. We also investigate the effects of the magnetic interaction J on the metal-charge-transfer-insulator transition. Allowing for the fl uctuations of the boson fields we show that this transition can still be characterized by the softening of the excitonic mode. The analysis of the Drude spectral weight, the specific heat, the compressibility, and the magnetic susceptibility is finally carried out to leading orde r in 1/N in the uniform Fermi-liquid phase at zero and low temperature . We calculate the different Landau parameters renormalizing the vario us quantities.