Helicity-Resolved Vibrational Coupling in Twist WS2/WSe2 Heterostructures

Helicity-resolved Raman spectra can provide an intricate view into lattice structural details. Through the analysis of peak positions, intensities, and circular polarized Raman signals, a wealth of information about chiral structure arrangement within the moiré superlattice, interlayer interaction strength, polarizability change in chemical bond, and beyond can be unveiled. However, the relationship between the circular polarization of high-frequency Raman and twist angle is still not clear. Here, we utilize helicity-resolved Raman spectroscopy to explore the interlayer interactions and the effect of the moiré superlattice in WS₂/WSe₂ heterostructures. For the out-of-plane Raman mode A_1g of WS₂ (A_1g and ¹E_2g of WSe₂), its intensity is significantly enhanced (suppressed) in WS₂/WSe₂ heterostructures when θ is less than 10° or greater than 50°. This observation could be attributed to the large polarizability changes in both W-S and W-Se covalent bonds. The circular polarization of 2LA(M) in WSe₂ of the WS₂/WSe₂ heterostructure (θ < 10° or θ > 50°) is significantly enhanced compared to that of 2LA(M) in the monolayer WSe₂. We deduce that the circular polarization of the Raman mode correlates with the proportion of high-symmetry area within a supercell of the moiré lattice. Our findings improve the understanding of twist-angle-modulated Raman modes in TMD heterostructures.