Dark exciton-exciton annihilation in monolayer WSe2

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 WSe2. 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.

Automated summary

This study demonstrates the key role of dark intervalley states in monolayer WSe2 in governing the exciton-exciton annihilation process, and reveals a characteristic temperature dependency of Auger scattering in this class of materials with excellent agreement between theory and experiment. The research provides microscopic insights into the efficiency of technologically relevant Auger scattering channels within atomically thin semiconductors' remarkable exciton landscape.