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 thed-wave form(coskx-cos⁡ky). Our findings provide a new theoretical perspective for understanding superconductivity in iron-based systems.