Polarized Moiré Phonon and Strain-Coupled Phonon Renormalization in Twisted Bilayer MoS2

Abstract

The ability to control the atomic-scale behavior in quasi-two-dimensional crystals via twisting the vicinal layers and generating patterned moiré potentials provides an additional degree of freedom to study correlated physics. Under the existence of macroscopic external parameters such as strain, we study the high-frequency Raman active vibrational modes of chemical vapor deposition (CVD)-grown monolayer, stacked (AA′ and AB), and twisted bilayer MoS2. The polarized Raman scattering, being an efficient characterization tool for these moiré structures, is employed to investigate the effects of strain on the different phonon modes. The recently discovered moiré phonons (FA1g), i.e., zone center phonons in a twisted bilayer MoS2, stem from the folding of the off-center phonons of its monolayer constituents and are found to be Raman polarized. Moreover, the Raman shift impressions of these moiré phonons in twist angle in the range between 0 and 30° are reproduced, showing the strain-coupled modifications of the previously reported sinusoidal behavior. Our findings establish an effective method to probe the strain-induced anisotropy in twisted van der Waals systems using polarized Raman spectroscopy showing future directions to moiré-related physics.