On the carrier spectrum of CuO2 planes in high-Tc superconductors and its dependence on stoichiometry

An attempt is made to analyse the problem of the conduction band type (σ or π) in HTSC copper oxides. It is established that the σ-character of this band may take place only under the condition of strong pd-hybridization between p- and d-holes from the upper Hubbard subband. The effect of nonstoichiometry on delocalized carriers consists in a possible appearence of discrete levels or a change in the spectrum as a whole. The estimate of thes carriers damping as a function of nonstoichiometry shows that the damping may be a nonmonotonous function of doping that makes it possible to speculate of various HTSC properties dependent on lattice disordering. (orig.)