Momentum-resolved observation of exciton formation dynamics in monolayer WS${}_2$

Abstract

The dynamics of exciton formation in transition metal dichalcogenides is difficult to measure experimentally, since many momentum-indirect exciton states are not accessible to optical interband spectroscopy. Here, we combine a tuneable pump, high-harmonic probe laser source with a 3D momentum imaging technique to map photoemitted electrons from monolayer WS${}_2$. This provides momentum-, energy- and time-resolved access to excited states on an ultrafast timescale. The high temporal resolution of the setup allows us to trace the early-stage exciton dynamics on its intrinsic timescale and observe the formation of a momentum-forbidden dark K$\Sigma$ exciton a few tens of femtoseconds after optical excitation. By tuning the excitation energy we manipulate the temporal evolution of the coherent excitonic polarization and observe its influence on the dark exciton formation. The experimental results are in excellent agreement with a fully microscopic theory, resolving the temporal and spectral dynamics of bright and dark excitons in WS${}_2$.

arXiv comment18 pages, 5 figures

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• Exciton-Driven Renormalization of Quasiparticle Band Structure in Monolayer MoS2
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• Probing correlations in the exciton landscape of a moiré heterostructure
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• Optical Signatures of Moiré Trapped Biexcitons
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• Hybrid Frenkel-Wannier excitons facilitate ultrafast energy transfer at a 2D-organic interface
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• Coherence and de-coherence in the Time-Resolved ARPES of realistic materials: an ab-initio perspective
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• Observation of quasi-steady dark excitons and gap phase in a doped semiconductor
• Dimensionality-Dependent Exciton Dispersion in a Single-Band Mott Insulator
• Effects of Strain-Induced Pseudogauge Fields on Exciton Dispersion, Transport, and Interactions in Transition Metal Dichalcogenides Nanoribbons
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• Ultrafast Charge Transfer Dynamics at the MoS${}_2$/Au Interface Observed via Optical Spectroscopy under Ambient Conditions