Phonon Sidebands in Transition Metal Dichalcogenides

TL;DR

This paper investigates how exciton-phonon interactions in monolayer transition metal dichalcogenides create asymmetric spectral features and phonon sidebands, enhancing understanding of their optical properties.

Contribution

It provides a combined theoretical and experimental analysis of phonon-induced sidebands and their microscopic origins in TMDs, including intra- and intervalley scattering mechanisms.

Findings

Identification of phonon sidebands causing spectral asymmetry

Demonstration of exciton-phonon coupling leading to polaron redshift

Insights into scattering channels in different TMD materials

Abstract

Excitons dominate the optical properties of monolayer transition metal dichalcogenides (TMDs). Besides optically accessible bright exciton states, TMDs exhibit also a multitude of optically forbidden dark excitons. Here, we show that efficient exciton-phonon scattering couples bright and dark states and gives rise to an asymmetric excitonic line shape. The observed asymmetry can be traced back to phonon-induced sidebands that are accompanied by a polaron redshift. We present a joint theory-experiment study investigating the microscopic origin of these sidebands in different TMD materials taking into account intra- and intervalley scattering channels opened by optical and acoustic phonons. The gained insights contribute to a better understanding of the optical fingerprint of these technologically promising nanomaterials.