ON THE HOLE SPECTRAL-FUNCTION OF THE EMERY MODEL

We discuss the spectral function of a single O hole generated in a two-dimensional CuO2-lattice at half-filling. The latter constitutes the most important structural element of high-Tc superconducting materials. The system is described by the so-called extended Hubbard or Emery model. Strong electronic correlations which are incorporated in the model prevent the usual evaluation of Green functions based on Wick's theorem and using diagram techniques. For that reason we apply a new cumulant approach to dynamical correlation functions introduced recently. As a result we find that the local one-O hole excitation spectrum has two structured absorption regions around the bare O energy e{open}p and around e{open}p+Δ due to charge fluctuations of Cu holes. Here Δ is the bare charge transfer gap. The width of the absorption regime around e{open}p is of the order of several times tpd2/Δ, where tpd is the hopping integral between Cu and O holes. © 1990 Springer-Verlag.