Enhanced superconductivity induced by nematic fluctuations in a two-orbital iron-based Hubbard model

To elucidate the relationship between nematicity and superconductivity in iron-based superconductors,we introduce a new type of electron-correlation term in a two-orbital Hubbard model, referred to as the off-site nematic interaction. Using quantum Monte Carlo simulations, we show that the off-site nematic interaction markedly suppresses nematic fluctuations near (π, π) while strongly enhancing those near (0, 0) in both hole-and electron-doped regimes. Concurrently, it reduces the (π, 0)/(0, π) antiferromagnetic structure factor. Most importantly, the combined effect of on-site and off-site nematic interactions establishes that (0, 0)-centered nematic fluctuations significantly enhance superconducting pairing, whereas (π, π)-centered fluctuations exert a weakly suppressive effect. Furthermore, our results reveal an intimate link between nematic fluctuations and superconducting pairing symmetry, with the most pronounced changes occurring in the d-wave form (cos kx -cos ky). Our findings provide a new theoretical perspective for understanding superconductivity in iron-based systems.