Three-band t-J model: A systematic large-N analysis.

Abstract

We investigate the physical properties of a three-band generalized t-J model within a systematic large-N slave boson approach allowing for dimer, flux, and uniform magnetic order. The mean-field (N=\ensuremath{\infty}) phase diagrams are characterized by the presence of phase separation, resulting from the competition of kinetic and magnetic energy, which is not spoiled by the inclusion of a direct oxygen-oxygen hybridization term, or of a copper-oxygen short-range Coulombic interaction term, and could be of some relevance in the description of the high-temperature superconducting cuprates. However, such a phase separation takes place between a magnetic dimer insulating phase and a metallic phase with flux order, which is not experimentally observed. The question of the stability of such an exotic phase is addressed in detail showing that the stability region of the flux phase can be greatly reduced especially by removing the nesting in the uniform Fermi-liquid phase and by the effects of the temperature. This scenario leaves open the possibility of an electronic origin of the phase separation observed in the cuprates. We also investigate the effects of the magnetic interaction J on the metal-charge-transfer-insulator transition. Allowing for the fluctuations 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 order in 1/N in the uniform Fermi-liquid phase at zero and low temperature. We calculate the different Landau parameters renormalizing the various quantities.