Distinctive characteristics of exciton-phonon interactions in optically driven MoS2

Polarized Raman spectroscopy offers the capability to study the interactions between electrons/excitons and phonons in the presence of intervalley scattering within two-dimensional materials. This study explores the relation between phonon symmetry and exciton-phonon interactions in monolayer and bilayer MoS2 using polarization-resolved photoluminescence and Raman spectroscopy. The resonant second-order Raman spectra in MoS2 are closely tied to material properties and laser excitation energy. Experimental and numerical analyses systematically examined phonon symmetry in Raman scattering, revealing a strong correlation between phonon symmetry and spin-valley polarization, especially under resonant excitation. Resonant excitation changed Raman scattering polarization because of the dominant Fröhlich interaction. The strong spin-orbit coupling in monolayer MoS2 unaffected by thermal vibrations at low temperatures leads to a notable increase in the valley polarization resulting from the restricted energy-level distribution of electron transitions. This phenomenon significantly influences the b mode in second-order resonant Raman scattering, consequently altering the chirality of phonon vibrations. We further propose a mechanism diagram elucidating the interaction between electrons and excitons of intervalley scattering. The study highlights the interplay between electron transitions and phonon-related behaviors in MoS2, emphasizing the significance of electron/exciton-phonon interactions under varying excitation energies and temperatures. These insights hold crucial implications for the optoelectronic applications of MoS2.