Magnetic and charge-transfer phase separation in the three-band t-J model.

Abstract

We investigate the physical properties of a three-band generalized Hubbard model for the ${\mathrm{CuO}}_{2}$ planes of high-${\mathit{T}}_{\mathit{c}}$ superconducting cuprates, in the presence of Cu-Cu superexchange and Cu-O Coulombic interaction. The explicit introduction of these interaction terms emphasizes the different role of spin and charge degrees of freedom in determining the behavior of the system. In particular, they provide two different mechanisms for phase separation, which are more effective in different doping regions. Experimental indications for this to occcur are discussed. We infer that magnetic and charge-transfer pairing interactions are related to the above phase-separation mechanisms and, while being simultaneously present, gradually interchange their relevance, the first one being dominant at low and intermediate doping, and the second one at high doping.