Exciton regulation of resonant Raman scattering in monolayer MoS₂

Strong excitonic effects in 2D semiconductors such as monolayer MoS₂ not only downshift its excitation spectrum from a single-particle one, but also redistribute excitation levels and wavefunction characters that profoundly affect exciton-phonon scattering processes, leaving strong signatures in resonant Raman measurements. We present a first-principles GW-Bethe-Salpeter equation (GW-BSE) approach based on perturbation theory to calculate resonant Raman intensities beyond the Placzek approximation. We show how excitonic effects in MoS₂ strongly regulate Raman scattering amplitudes and explain two puzzling experimental observations: the near absence of Raman response at the A and B band-edge excitons and the pronounced strength of Raman response near the C exciton. This perturbative approach reduces the number of GW-BSE calculations from two per Raman mode in finite displacement methods to one for all modes and allows a natural extension to higher-order resonant Raman processes [Phys. Rev. B 98, 161405 (2018)].