The energy dispersion of the singlet correlated impurity band in layered cuprates

The Green's function method is applied to the calculation of the low energy spectrum in layered cuprates using Hubbard projection operators. Hund's and Kondo-like exchange, copper-oxygen and oxygen-oxygen hopping are taken into account. An analytical expression for the impurity band has been obtained. This expression is analyzed in connection with considerations of Zhang and Rice, Matsukawa and Fukuyama and others that serve as the basis of the so-called t-J model. © 1993