HOLE PAIRING SYMMETRY IN ATTRACTIVE HUBBARD-MODEL

Geometrical effects on the pairing process between electrons and betwe en holes are comparatively studied by using an attractive Hubbard Hami ltonian. For triangular lattices, it is found that the hole pairing is always stronger than the electron case due to the frustration of anti -bonding states; contrary to that occurred in bipartite lattices, wher e there is a complete symmetry between the electron and hole pairings. The ground state of two holes, when the attractive nearest-neighbor i nteraction is dominant, is surprisingly triplet and its wave function has directional nodes. On the other hand, the hole pairing in disorder ed lattices is analyzed and the results show an enhancement of the pai r-binding energy as the self-energy difference increases in a random b inary alloy A(x)B(1-x). This fact suggests that the pairing process is highly sensitive to the one-particle localization condition. The grou nd-state phase diagram for the case of on-site interaction disorder sh ows regions where pairing is avoid for ordered diatomic systems but no t for disordered cases.