Dependence of the polarizability of the Cu₄O₈ cluster on the doping, the weight of the oxygen-hole state, and the excitation gaps in the three-band Hubbard model

Abstract

We have obtained the model exact static polarizability of the Cu₄O₈ cluster within the three-band Hubbard model for different doping levels. The excitation gaps as well as the weight of the O^- (oxygen-hole) state in the ground-state wave function have been exactly computed. The parameters of the model are varied to alter the excitation gaps as well as the weight of the O^- state in order to examine the dependence of the polarizability on these quantities. The Cu₄O₈ cluster is highly polarizable, the polarizability increasing with the doping level. The polarizability is large when the excitation gap is charge-transfer-like and increases with the decreasing gap; it also increases markedly with the increase in the weight of the O^- state. Experimentally, the T_c in the cuprates is highest for the range of the weight of O- for which the lattice is highly polarizable.