ENHANCED HOLE PAIRING IN GENERALIZED HUBBARD SYSTEMS

The pairing between holes at the dilute limit is studied by means of a generalized Hubbard model, in which on-site (U), nearest-neighbor (V) and correlated-hopping (Delta t) interactions are considered. The pro blem is addressed by mapping the original many-body problem into a tig ht-binding one in a higher dimensional space. The results show a stron g enhancement of the hole pairing around Delta t/t(0) = 0.5, even thou gh the on-site or nearest-neighbor repulsion is extremely high. A sign ificant reduction of the effective mass of pairs in comparison with no n-pairing ones is also observed in this region, which could be importa nt in the Bose-Einstein condensation of these hole singlets. Finally, the pairing phase diagrams calculated in linear, square, triangular an d cubic lattices show an enhanced hole pairing in low-dimensional syst ems. (C) 1998 Elsevier Science Ltd. All rights reserved.