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.
Highlights
Thin nanomaterials, such as transition-metal dichalcogenides (TMDs), offer an unprecedented platform to study intriguing many-particle phenomena in a broad range of external conditions [1,2,3,4]
Excitons can interact through exciton-exciton annihilation (EEA), an Auger-like recombination process limiting the efficiency of optoelectronic applications
Excitons can interact through exciton-exciton annihilation (EEA), an Auger recombination process shown to be very efficient in TMDs [5,6,7,8]
Summary
Thin nanomaterials, such as transition-metal dichalcogenides (TMDs), offer an unprecedented platform to study intriguing many-particle phenomena in a broad range of external conditions [1,2,3,4]. Recent up-converted photoluminescence (PL) measurements and ab initio calculations confirmed the existence of a higher energetic exciton state appearing at approximately twice the A exciton resonance both in monolayer and bilayer WSe2 [10,17] This can be attributed to the existence of higherlying conduction bands, enabling a particular type of resonant Auger scattering [9,18,19], cf Fig. 1. Since the energetically lowest states of tungsten-based TMDs are dark [24,26,27,28], one would expect intervalley exciton-exciton Auger recombination processes [II, III in Fig. 1(b)] to be relevant In this joint theory-experiment study, we address the nature of Auger-like exciton-exciton annihilation in atomically thin semiconductors by combining time- and temperature-resolved PL measurements with material-specific microscopic modeling including density matrix and density functional theory methods. Our calculations provide insight into the previously observed decrease of Auger scattering for hBNencapsulated WSe2 and WS2 monolayers [20,22,23] and we explain this effect with the changed resonance condition within the excitonic bandstructure
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
