Revisiting the Quasiparticle Band Structure and Optical Properties of Few‐Layer InSe

The many‐body GW combined with the Bethe–Salpeter equation (BSE) method including the spin‐orbit coupling (SOC) effect has been adopted to revisit the band structure and optical absorption spectra evolution of single‐layer, double‐layer, three‐layer, and bulk InSe. The many‐body effect is found to play an important role in both the band structure and the optical properties of InSe structures. Not only the band gap but also the energy dispersion is influenced by the electron–electron many‐body interaction. Electron–hole interaction strongly affects the optical properties of InSe structures, especially the single‐layer InSe. Compared with previous reports, the calculations show that, including SOC, two bound excitonic peaks have emerged for monolayer InSe, with the strong bound exciton being s‐state‐like, while the other p‐state‐like. BSE also predicts abundance of bounded “dark” excitons exists for monolayer InSe, indicating that monolayer InSe is a proper platform for studying excitons. Although the spin‐orbit interaction influence on the highest valence band and the lowest conducted band seems trivial, its effect on the optical properties of InSe is remarkable.