M. Cini et A. Balzarotti, HOLE PAIRING AND FLUX-QUANTIZATION IN MODEL CU-O CLUSTERS, Nuovo cimento della Societa italiana di fisica. D, Condensed matter,atomic, molecular and chemical physics, biophysics, 20(7-8), 1998, pp. 1141-1146
In the three-band Hubbard model, the fully symmetric Cu-O clusters wit
h a central Cu and appropriate hole numbers have many-body ground stat
es in which holes are paired. Here we investigate the mechanism of pai
ring, focusing on clusters with less than or equal to 21 atoms and 4 h
oles. We show that spin-flip diagrams yield the effective interaction.
The analysis agrees with the results of exact diagonalization and sho
ws that singlet-triplet splitting measures the strength of the pairing
interaction. Moreover the quantization at half-integer values of a ma
gnetic text flux is consistent with superconducting pairing.