Symmetry-Controlled Electron-Phonon Interactions in van der Waals Heterostructures.

Abstract

Light-matter interactions in the van der Waals (vdWs) heterostructures exhibit many fascinating properties which can be harnessed to realize optoelectronic applications and probe fundamental physics. Moreover, the electron-phonon interaction in the vdWs heterostructures can have a profound impact on light-matter interaction properties because light excited electrons can strongly couple with phonons in heterostructures. Here, we report symmetry-controlled electron-phonon interactions in engineered two-dimensional (2D) material/silicon dioxide (SiO2) vdWs heterostructures. We observe two Raman modes arising from originally Raman-silent phonon modes in SiO2. The Raman modes have fixed peak positions regardless of the type of 2D materials in the heterostructures. Interestingly, such Raman emissions exhibit various symmetry properties in heterostructures with 2D materials of different crystalline structures, controlled by their intrinsic electronic band properties. In particular, we reveal chiral Raman emissions with reversed helicity in contrast to that of typical valley polarization in honeycomb 2D materials due to the phonon-assisted excitonic intervalley scattering process induced by electron-hole exchange interaction. The observation of the symmetry-controlled Raman scattering process not only provides a deep insight into the microscopic mechanisms of electron-phonon interactions in vdWs heterostructures but also may lead to the realization of valley-phononic devices.