Superconductivity and density-wave fluctuations in an extended triangular Hubbard model: an application to SnSe.

We employ the fluctuation-exchange approximation to study the relation of superconducting pairing symmetries and density-wave fluctuations based on the extended triangular Hubbard model upon electron doping and interactions, with an possible application to the layered metal dichalcogenide SnSe. For the case where the interactions between electrons contain only the on-site Hubbard term, the superconducting pairings are mainly mediated by spin fluctuations, and the spin-singlet pairing with the-wave symmetry robustly dominates in the low and moderate doping levels, and a-wave to extended-wave transition is observed as the electron doping reaches = 1. When the near-neighbor site Coulomb interactions are also included, the charge fluctuations are enhanced, and the spin-triplet pairings with the-wave and-wave symmetries can be realized in the high and low doping levels, respectively.