Optimal inhomogeneity for pairing in Hubbard systems with next-nearest-neighbor hopping

Previous studies have shown that bipartite Hubbard systems with inhomogeneous hopping amplitudes can exhibit higher pair-binding energies than the uniform model. Here we examine whether this result holds for systems with a more generic band structure. To this end, we use exact diagonalization and the density matrix renormalization-group method to study the 4×4 Hubbard cluster and the two-leg Hubbard ladder with checkerboard-modulated nearest-neighbor hopping, t, and next-nearest-neighbor (diagonal) hopping, td. We find that the strongest pairing continues to occur at an intermediate level of inhomogeneity. While the maximal pair-binding energy is enhanced by a positive td/t, it is suppressed and appears at weaker repulsion strengths and lower hole concentrations when td/t is negative. We point out a possible connection between the pairing maximum and the magnetic properties of the system.