Bruno R. Carvalho ; Yuanxi Wang ; Sandro Mignuzzi ; Debdulal Roy ; Mauricio Terrones ; Cristiano Fantini ; Vincent H. Crespi ; Leandro M. Malard ; Marcos A. Pimenta
Double-resonance Raman (DRR) scattering is a sensitive probe to study the electron-phonon scattering pathways in crystals. For semiconducting two-dimensional transition-metal dichalcogenides, the DRR process has not been fully understood yet, and it involves different valleys and phonons in the Brillouin zone. Here, we present a multiple energy excitation Raman study in conjunction with density functional theory calculations that unveil the DRR scattering process in monolayer and bulk MoS2. Results show that the frequency of some Raman features shifts when changing the excitation energy and first-principle simulations confirm that these features arise from different acoustic phonons, connecting different valley states.
The DRR process is affected by the indirect-to-direct bandgap transition and a detailed comparison of results in monolayer and bulk allow the assignment of each Raman feature to specific phonons near M or K. Our work highlights intervalley scattering by acoustic phonons, which is essential for valley depolarization in MoS2.