dx2–y2 pairing in the generalized Hubbard square-lattice model

The pairing between holes in a square lattice and the two-particle wave-function symmetry are studied within a generalized Hubbard model. The key participation of the next-nearest-neighbor correlated-hopping interaction in the appearance of d-wave two-hole ground state is found, which is enhanced by the on-site repulsive Coulomb interaction. There is a clear pairing asymmetry between electrons and holes, where the hole pairing occurs in a realistic regime of interactions. The two-particle states are analyzed by looking at the binding energy, the coherence length, and the effective mass of the pairs. Finally, the case of a hole-singlet in an antiferromagnetic background is also studied.