Exciton-Driven Renormalization of Quasiparticle Band Structure in Monolayer MoS2

TL;DR

This study demonstrates that excitonic correlations can directly cause bandgap opening and effective mass enhancement in monolayer MoS2, revealing a new mechanism for optical band structure control in layered semiconductors.

Contribution

It provides the first direct experimental evidence of exciton-driven band renormalization in a monolayer semiconductor using advanced spectroscopy and theoretical calculations.

Findings

Bandgap increased by 40 meV due to excitonic effects

Simultaneous enhancement of band effective mass observed

Revealed a novel exciton-driven band engineering mechanism

Abstract

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.