Electronic States and Charge Fluctuation on the CuO₂-2D Lattice

Abstract

Electronic states and charge fluctuation on 2D CuO₂ lattice with the infinite repulsion on the Cu-sites are investigated with auxiliary boson technique and the l/N expansion method. It is shown that, for a large charge transfer energy, the undoped system is insulating, and that, upon doping, mid- gap states are generated inside the charge transfer gap. Effects of repulsion U _pd between Cu- and O-holes on the mid-gap states are then studied. There are two characteristic values of U^I _pd : One is which makes the undoped system with a small charge transfer energy insulating. The other is U^c _pd at which value the charge susceptibility diverges; this implies an instability toward phase separation. The enhanced charge susceptibility may be the driving force of the superconducting instability.