Probing the Role of Dark Excitons in Twist-Angle-Dependent Transport Dynamics in WS<sub>2</sub>/WSe<sub>2</sub> via Time-Resolved ARPES
ORAL
Abstract
The periodic moiré potential in twisted van der Waals materials has emerged as a new platform for tailoring exciton states. Interlayer excitons (IXs), formed by electrons and holes residing in different layers of TMDC heterostructures, can be further modulated by moiré potential, forming moiré excitons with new exciton physics. However, a full understanding of the moiré exciton requires access to momentum-dark states that significantly influence exciton formation, decay dynamics, and exciton transport. Recently, momentum-dark states have been invoked to explain the twist-angle-dependent diffusion of excitons in WS2/WSe2 bilayers [1]. However, optical measurements were unable to directly observe these dark states. Optically dark excitons in 2D materials can be observed via time- and angle-resolved photoemission [2]. In this work we apply time-resolved momentum microscopy with XUV pulses at 61 MHz repetition rate [3] to observe the dark state population in WS2/WSe2 while varying both the twist angle and the temperature. We compare our results to previous modeling of optical spectroscopy and exciton diffusion.
*This work was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under award number DE-SC0022004 and the Air Force Office of Scientific Research under FA9550-20-1-0259.
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Publication: [1] L. Yuan et al. Twist-angle-dependent interlayer exciton diffusion in WS2 –WSe2 heterobilayers. Nature Materials 19, 617 (2020)
[2] J. Madeo. Directly visualizing the momentum-forbidden dark excitons and their dynamics in atomically thin semiconductors. Science 370, 1199 (2020).
[3] Kunin, A., et al. Momentum-resolved Exciton Coupling and Valley Polarization Dynamics in Monolayer WS2. Phys. Rev. Lett. 2023, 130, 046202.
Presenters
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Jianwei Ding
- Stony Brook University (SUNY)