Optical absorption in the two-dimensional two-band model

Abstract

The optical properties are studied within the two-dimensional two-band model with the antiferromagnetic exchange interaction between nearest-neighbord andp spins in the Cu-O sheet. The optical-absorption spectra are computed within the mean-field theory with the periodic boundary condition. An insulating gap of about 1.7 eV appears for nondoping. A Drude peak appears for a singlep hole. The Drude peak and the in-gap state appear for twop holes. The intensity of the charge-transfer band decreases, while those of the Drude peak and the in-gap state increase with doping. It turns out that the strong Coulomb repulsion and the$d_{x^2 - y^2 }$ orbital are important such as thep _x orp _y orbital in the electronic properties of high-T _c copper oxides.