  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.
