SPIN AND CHARGE FLUCTUATION IN AN EXTENDED HUBBARD-MODEL OF OXIDE SUPERCONDUCTORS

Antiferromagnetic spin fluctuations and charge-transfer correlation are studied in an extended Hubbard model of cuprate superconductors. We have carried out finite-temperature Monte Carlo and variational Monte Carlo simulations Of CuO2 lattices described by a three-band Hubbard model. Using parameters derived by local-density-functional theory, our results appear to be consistent with experimental data. At half-filling, we find strong antiferromagnetic correlation with large local moment on copper sites and evidence of a charge-transfer gap. Upon doping, the antiferromagnetic correlations decrease; the excess holes primarily go onto the oxygen sites, while additional electrons prefer the copper sites. Equal-time pairing correlation functions suggest that extended s-wave and d-wave pairing are possible in this model.