BAND CROSSING AND NOVEL LOW-ENERGY BEHAVIOR IN A MEAN-FIELD THEORY OFA 3-BAND MODEL ON A CU-O LATTICE

We study correlation effects in a three-band extended Hubbard model of Cu-O planes within the 1/N mean field approach in the infinite LI lim it. We investigate the emerging phase diagram and discuss the low ener gy scales associated with each region. With increasing direct overlap between oxygen orbitals, t(pp) > 0, the solution displays a band cross ing which, for an extended range of parameters, lies close to the Ferm i level. In turn this leads to the nearly nested character of the Ferm i surface and the resulting linear temperature dependence of the quasi -particle relaxation rate for sufficiently large T. We also discuss th e effect of band crossing on the optical conductivity and comment on t he possible experimental relevance of our findings.