Ultrafast Insights into High Energy (C and D) Excitons in Few Layer WS2

High energy (C and D) excitons possess extraordinary influence over the optical properties of atomically thin transition metal dichalcogenides (TMDCs), and the comprehensive understanding of these would play a pivotal role in advancing research on 2D optoelectronics. Herein, we employed transient absorption spectroscopy to monitor the underlying photophysical processes involved with different excitonic features in few layer WS2, modeled as a TMDC representative. We observed a strong intervalley coupling across the momentum space and proposed the most plausible relaxation pathway for different excitons in few layer scenario. C and D exciton dynamics were significantly slower as compared to canonical A and B excitons, as a consequence of the indirect Lambda-Gamma relaxation in C and D and direct K-K combination in A and B. Most importantly, all four excitons emerge in the system and influence each other irrespective of the incident photon energy, which would be extremely impactful in fabricating wide range photonic devices.

Automated summary

This study employed transient absorption spectroscopy to investigate the optical processes related to different excitonic features in few layer WS2, a TMDC representative. It revealed a strong intervalley coupling across the momentum space and slower dynamics for C and D excitons compared to A and B excitons. All four excitons were observed to emerge in the system and influence each other, regardless of the incident photon energy.