Kavli Affiliate: Alessandra Lanzara
| First 5 Authors: Yi Lin, Yang-hao Chan, Woojoo Lee, Li-Syuan Lu, Zhenglu Li
| Summary:
Optical excitation serves as a powerful approach to control the electronic
structure of layered Van der Waals materials via many-body screening effects,
induced by photoexcited free carriers, or via light-driven coherence, such as
optical Stark and Bloch-Siegert effects. Although theoretical work has also
pointed to an exotic mechanism of renormalizing band structure via excitonic
correlations in bound electron-hole pairs (excitons), experimental observation
of such exciton-driven band renormalization and the full extent of their
implications is still lacking, largely due to the limitations of optical probes
and the impact of screening effects. Here, by using extreme-ultraviolet
time-resolved angle-resolved photoemission spectroscopy together with excitonic
many-body theoretical calculations, we directly unmask the band renormalization
effects driven by excitonic correlations in a monolayer semiconductor. We
revealed a surprising bandgap opening, increased by 40 meV, and a simultaneous
enhancement of band effective mass. Our findings unmask the novel
exciton-driven mechanism towards the band engineering in photoexcited
semiconducting materials, opening a new playground to manipulate the transient
energy states in layered quantum materials via optical controls of excitonic
many-body correlations.
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