Enhancing d-wave superconductivity with nearest-neighbor attraction in the extended Hubbard model

Motivated by the recent discovery of the anomalously nearest-neighbor attraction arising from the electron-phonon coupling, we quantitatively investigate the enhancing effects of this additional attractive channel on the d-wave superconductivity based on dynamic cluster quantum Monte Carlo calculations of a doped two-dimensional extended Hubbard model with nearest-neighbor attraction -V. Focusing on the range of 0<-V/t≤2, our simulations indicate that the dynamics of d-wave projected pairing interaction is attractive at all frequencies and increases with $|V|$. Moreover, turning on -V attraction enhances the (π,π) spin fluctuations but only enhances (suppresses) the charge fluctuations for small (large) momentum transfer. Thus, at V/t=-1 relevant to the ``holon folding branch'', the charge fluctuations are insufficient to compete with the d-wave pairing interaction strengthened by enhanced spin fluctuations. Our work suggests the underlying rich interplay between the spin and charge fluctuations in giving rise to the superconducting properties.