Emergent bright excitons with Rashba spin-orbit coupling in atomic monolayers

Optical properties in van der Waals heterostructures based on monolayer transition-metal dichalcogenides (TMDs) are often dominated by excitonic transitions. While intrinsic spin-orbit coupling (SOC) and an isotropic band structure are typically studied in TMDs, in their heterostructures Rashba SOC and trigonal warping (TW), resulting in bands with threefold anisotropy, are also present. By considering a low-energy effective Hamiltonian and Bethe-Salpeter equation, we study the effect of Rashba SOC and TW on the band structure and absorption spectra. Rashba SOC is predicted to lead to emergent excitons, which are identified as an admixture between $1s$ and $2p$ symmetries. In contrast, for experimentally relevant values, TW has only a negligible effect on the absorption spectrum. These findings could guide experimental demonstrations of emergent bright excitons and further studies of the proximity effects in van der Waals heterostructure.