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.
