PHASE-SEPARATION NEAR THE MOTT TRANSITION IN LA2-XSRXCUO4

Competition between the Mott transition and Fermi surface nesting in a Cu-O2 plane is studied in the limit of infinite on-site Coulomb repulsion. By incorporating direct O-O hopping, the nesting condition (Fermi surface at van Hove singularity) can be shifted away from half filling. The Mott transition (actually a transition to a charge transfer insulator) remains at half filling, driven by electron correlation effects, herein described via a slave boson formalism. Away from half-filling, electron-phonon coupling leads to a phase separation into the insulating phase near half filling, and a metallic phase close to the van Hove singularity. The consequences of this phase separation for high-Tc superconductivity are briefly discussed.