Symmetry breaking of in-plane Raman scattering by elliptically polarized light in MoS2

The breaking of the doubly degenerate in-plane lattice vibrations in monolayer, bilayer, and bulk molybdenum disulfide (${\mathrm{MoS}}_{2}$) are oftentimes ignored in the analysis of the material's lattice behaviors due to the lack of variation of polarization for the excitation light. In this work, we have observed variations in the relative intensity of the two most dominant Raman peaks of ${\mathrm{MoS}}_{2}$ via polarized micro-Raman spectroscopy using elliptically polarized incident light. The use of elliptically polarized light has demonstrated distinct properties in its incident Raman polarization vector. This gives an additional degree of freedom affecting the relationship between the $x$ (${E}_{2gx}^{1}$) and $y$ (${E}_{2gy}^{1}$) components of the material's in-plane lattice vibrations. The different ratio of the magnitudes for the ${E}_{2gx}^{1}$ and ${E}_{2gy}^{1}$ in the lattice vibrations can be induced by changing the polarization state of the incident light. This work investigates the material's unexplored fundamental phonon property that may enlighten past and future studies involving phonon behaviors.