Dark exciton-exciton annihilation in monolayer WSe$_2$

TL;DR

This study combines theory and experiments to reveal that dark intervalley exciton states dominate exciton-exciton annihilation in monolayer WSe2, showing a temperature-dependent Auger process crucial for optoelectronic applications.

Contribution

It provides the first microscopic understanding of dark exciton states' role in exciton-exciton annihilation in monolayer WSe2, integrating theory with temperature-resolved photoluminescence data.

Findings

Dark intervalley states dominate EEA rate in WSe2.

Temperature dependence of Auger scattering matches theory.

Microscopic insights into exciton interactions in 2D semiconductors.

Abstract

The exceptionally strong Coulomb interaction in semiconducting transition-metal dichalcogenides (TMDs) gives rise to a rich exciton landscape consisting of bright and dark exciton states. At elevated densities, excitons can interact through exciton-exciton annihilation (EEA), an Auger-like recombination process limiting the efficiency of optoelectronic applications. Although EEA is a well-known and particularly important process in atomically thin semiconductors determining exciton lifetimes and affecting transport at elevated densities, its microscopic origin has remained elusive. In this joint theory-experiment study combining microscopic and material-specific theory with time- and temperature-resolved photoluminescence measurements, we demonstrate the key role of dark intervalley states that are found to dominate the EEA rate in monolayer WSe$_2$. We reveal an intriguing, characteristic temperature dependence of Auger scattering in this class of materials with an excellent agreement between theory and experiment. Our study provides microscopic insights into the efficiency of technologically relevant Auger scattering channels within the remarkable exciton landscape of atomically thin semiconductors.