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【Abstract】

The tightly bound excitons in two-dimensional (2D) materials have garnered considerable interest for their remarkable optical, spintronic, and valleytronic properties. Although brightly luminescent excitons, which couple directly with light, have been thoroughly investigated for their effective light-matter interactions, dark excitons are less explored. Nonetheless, dark excitons display distinctive physical properties such as prolonged population lifetimes and extended diffusion lengths, vital for manipulating exciton dynamics in practical devices. Understanding and controlling bright and dark excitons is essential for examining many-body Coulomb interactions and advancing exciton-based technologies with innovative functionalities.
In my talk, I will explore the many-body interactions of dark excitons in 2D transition metal dichalcogenides through optical spectroscopy. Our studies have identified dark-exciton-mediated biexcitons and exciton-trions in high-quality monolayer WSe2 devices, revealing substantial interactions between bright and dark excitons and emphasizing the critical role of dark excitons in these systems. Furthermore, we have observed that dark excitons can facilitate efficient light upconversion through exciton-exciton annihilation. This discovery opens new avenues for manipulating dark excitons and potentially enhances their application in nanophotonic 2D-material-based photovoltaic and photocatalytic technologies.