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Exciton-driven two-step charge transfer in MoS2-WSe2 heterostructures revealed by valley-resolved broadband
Zi-Fan Hu1, Ting-Ting Wang1, Yu-Peng Zhang1
1State Key Laboratory of Integrated Optoelectronics, JLU Region, College of Electronic Science and Engineering, Jilin University, Changchun 130012, China. Haiyu_wang@jlu.edu.cn.
Abstract:
The strong excitonic effects in transition metal dichalcogenide (TMD) heterostructures (HSs) play a critical role in interlayer charge transfer. Using valley-resolved broadband pump-probe spectroscopy, we investigate the charge dynamics in MoS2-WSe2 HSs. Electrons transferred from WSe2 to MoS2 exhibit delayed valley polarization build-up, indicating a two-step process: initial population of a high-energy spin-degenerate state in MoS2via transition from WSe2 intralayer excitons to hot interlayer excitons, followed by sub-picosecond relaxation into lower-energy states. Holes in WSe2 show analogous relaxation dynamics, corresponding to the relaxation of interlayer excitons. Temperature-dependent measurements confirm that these processes are nearly insensitive to thermal variations, which align well with the Dexter-type electron exchange mechanism. Our findings underscore the role of excitons in enhancing interlayer coupling and enabling robust charge separation, demonstrating the capability of valley-resolved spectroscopy for probing ultrafast processes in TMD HSs.
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