SUPEREXCHANGE IN THE CUPRATES - A MEAN-FIELD STUDY

A three-band Hubbard Hamiltonian, which contains the direct O-O and Cu -O hopping, and the repulsion on the copper and oxygen and between the m, is employed to study superexchange in cuprates by using mean-field approximation. Our calculations show that the effect of O-O hopping an d Cu-O repulsion interaction on the superexchange is very considerable . Taking acceptable values of the model parameters, we obtain superexc hange constant J approximate to 0.12 eV in agreement with experimental result, and find that the contribution from O-O hopping is about 2/3 of the total value in accordance with exact cluster calculation. The p ressure-dependence of J is also discussed, and can qualitatively expla in the experiment. (C) 1998 Elsevier Science B.V. All rights reserved.