Giant valley polarization splitting and circular dichroism response in WS₂/CrBr₃ heterostructure via ultrafast spin-charge transfer

Manipulation of exciton dynamics is a fundamental approach for exploiting the valley degree of freedom in two-dimensional van der Waals (vdWs) heterostructures and developing high-performance valleytronic devices. Herein, we report a method for controlling interlayer spin-charge transfer in WS₂/CrBr₃ vdWs heterostructure through graphene proximity coupling and achieve a giant chirality-dependent valley polarization splitting. Theoretical and experimental findings reveal that the WS₂/CrBr₃ vdWs heterostructure retains its initial large conduction band offset under light irradiation when it is coupled with a few-layered graphene in the bottom. The interlayer spin-charge transfer time is significantly reduced from 17.3 to 1.3 ps, leading to a remarkable improvement in the valley polarization. The degree of valley polarization and polarization splitting of trion excitons in WS₂ are enhanced by 32% and 261%, respectively. Moreover, a highly sensitive circularly polarized photodetector was developed by using the WS₂/CrBr₃/graphene heterostructure. This work pioneers a route to efficiently manipulate the transport behavior of excitons in vdWs heterostructures and also offers a novel idea for designing high-performance spintronic devices.