Metal-Insulator Transition and Charge Fluctuationin the<i>d</i>-<i>p</i>Model

Abstract

Electronic states in the d-p model, particularly those around the half-filled case, are investigated with the help of the auxiliary boson method and the 1/ N -expansion. The critical value of the charge transfer energy for a metal-insulator transition to occur at the half-filled case is evaluated. The analytic expression for the charge susceptibility is given. Then characteristics of the charge fluctuation around the transition point are clarified; it is found that the charge susceptibility vanishes on the critical point. Furthermore, dependence of the charge susceptibility on the hole number and on the charge transfer energy is studied. Relevance to high temperature superconducting materials is then discussed.