Quasi-Nonvolatile Electrical Manipulation of Chiral Raman Signals

Quasi-nonvolatile electrical manipulation of the chiral Raman signals is demonstrated in a floating-gate device of a monolayer-WSe₂/h-BN/graphene heterostructure. The charge-storage layer of graphene can assist in quasi-nonvolatile control of the doping level of the monolayer WSe₂ under different electrical voltages, leading to the quasi-nonvolatile conversion between free and charged excitons. As a consequence, combining with the strong positive correlation between Raman scattering signal and free exciton density, the Raman signals can be efficiently switched on and off with a large on/off ratio via the conversion of exciton species by gate voltage. Importantly, benefiting from the presence of the chiral phonons in monolayer WSe₂, the Raman signals exhibit chirality and carry valley polarization information with a degree of circular polarization over 60% and a lower decoherence rate compared to excitons under circularly polarized light excitation, which thus can increase the encoding capability and be beneficial for robust high-temperature valleytronics.