HOLE PAIRING IN THE HUBBARD-MODEL

The hole-pairing problem at the dilute limit on low-dimensional bipart ite and non-bipartite lattices is studied by means of the generalized Hubbard model. in which on-site (U), nearest-neighbor (V), and assiste d-hopping (Delta t) terms are considered. The problem is addressed by mapping the original many-body problem onto a tight-binding one in a h igher-dimensional space. It is found that there is a small region arou nd Delta t/t(0) = 0.5, where the pairing of holes is enhanced and non- pairing of electrons exists. Pairing phase diagrams are analyzed for l inear, square and triangular lattices, in comparison with those result s obtained from the extended Hubbard model. (C) 1998 Elsevier Science B.V. All rights reserved.