Ultrafast Insight into High energy (C, D) Excitons in Few Layer WS2

TL;DR

This study uses transient absorption spectroscopy to explore high-energy C and D excitons in few-layer WS2, revealing their dynamics, inter-valley coupling, and influence on optical properties relevant for 2D opto-electronic devices.

Contribution

It provides new insights into the ultrafast dynamics and momentum space behavior of high-energy excitons in WS2, highlighting their complex interactions and relaxation pathways.

Findings

C, D excitons exhibit slower dynamics than A, B excitons due to indirect relaxation pathways.

Strong inter-valley coupling across momentum space was observed.

D excitons behave similarly to A, B, while C excitons depend on photon energy and band nesting.

Abstract

High energy (C, D) excitons possess remarkable influence over the optical properties of layered transition metal dichalcogenides (TMDCs) and comprehensive understanding of these may have revolutionary effect on 2D opto-electronic devices. Herein, we employed transient absorption spectroscopy to monitor the underlying photo-physical processes involved with C, D excitons in few layer WS2. We observed a strong inter-valley coupling across the momentum space. C, D dynamics were significantly slower as compared to canonical A, B excitons, as a consequence of the indirect Lambda-Gamma relaxation in C, D, unlike K-K direct combination in A, B. Optical behaviour of D excitons was found to be more like A, B, contrary to C, which enjoy unique band nesting effects. Also, C excitons do not hold in any specific position of the momentum space, rather depends upon the photon energy. All these excitons immensely influence each other irrespective of the excitation energy.