Observation of Dynamic Screening in the Excited Exciton States in Multi-layered MoS$_2$

TL;DR

This study reveals that the Coulomb screening effect in multi-layered MoS$_2$ excitons is frequency-dependent and dynamically modulated by ultrafast photo-excitation, affecting the excited states' properties.

Contribution

It demonstrates the dynamic, frequency-dependent screening effect on excited exciton states in multi-layered MoS$_2$, a novel insight into excitonic behavior under ultrafast excitation.

Findings

Resonance frequency determines screening efficacy for excited excitons.

Dynamic screening effects influence excitonic resonance properties.

Ultrafast photo-excitation modulates excitonic interactions.

Abstract

Excitonic resonance and binding energies can be altered by controlling the environmental screening of the attractive Coulomb potential. Although this screening response is often assumed to be static, the time evolution of the excitonic quasiparticles manifests a frequency-dependence in its Coulomb screening efficacy. In this letter, we investigate a ground (1s) and first excited exciton state (2s) in a multi-layered transition metal dichalcogenide (MoS$_2$) upon ultrafast photo-excitation. We explore the dynamic screening effects on the latter and show its resonance frequency is the relevant frequency at which screening from the smaller-sized 1s counterparts is effective. Our finding sheds light on new avenues of external tuning on excitonic properties.