d-Wave hole superconductivity in low-dimensional Hubbard systems

Superconducting states with d symmetry in anisotropic hole systems are investigated within a generalized Hubbard model and the BCS framework. The results reveal a key participation of the next-nearest-neighbor correlated-hopping interaction (Δt3) in the appearance of cos kx−cos ky superconducting gap, in spite of its small strength in comparison with other terms of the model. This interaction favors the superconducting state over the phase separation, which is an important obstacle when the d-wave superconducting state is originated from an attractive nearest-neighbor density–density interaction. Furthermore, the superconducting critical temperature is highly enhanced by the low-dimensionality of the system and the gap ratio exhibits a non-BCS behavior.