Interplay of valley selection and helicity exchange of light in Raman scattering for graphene and MoS2

Abstract

Raman spectra of graphene and ${\mathrm{MoS}}_{2}$ are calculated for incident and scattered circularly polarized light. In the case of graphene, the well known $G$-band Raman spectra have a not well known property that the helicity of the incident circularly polarized light changes to another helicity in the scattered light. Using the electron-photon and electron-phonon matrix elements by first-principles calculation, we calculate resonant Raman spectra of graphene and ${\mathrm{MoS}}_{2}$ for circularly polarized light which are compared with recent experiments. The Raman intensity for circularly polarized light is relevant to optical valley polarization in the case of ${\mathrm{MoS}}_{2}$. We also discuss how the helicity-selection rule can be modified by applying stress to graphene.