Abstract:
Tightly bound excitons in two-dimensional (2D) materials have attracted significant interest owing to their appealing optical, spintronic, and valleytronic properties. The most studied bright exciton can directly couple to the light and exhibit great light-matter interactions. On its dark side, the dark excitons are much less studied. Still, they have fascinating physical properties, such as a much longer population lifetime and diffusion length, critical for manipulating the exciton in functional devices. Effective manipulation of bright and dark excitons is urgently needed to understand many-body Coulomb interactions and develop exciton-mediated applications with new functionalities.
In this talk, I will unveil the dark excitons in 2D materials through photoluminescence spectroscopy. We observed dark-exciton-mediated biexciton and exciton-trions in high-quality monolayer WSe2 devices. The formation of these multi-particle states suggests the significant binding of the bright and dark excitons, highlighting the important roles of dark excitons in 2D systems. Moreover, I will demonstrate an interesting platform of atomically thin InSe for further manipulating dark excitons. We observed the long-lived dark excitons in monolayer InSe which can be efficient brightening through strong exciton-phonon coupling. Our results show the unique properties of such dark excitons in atomically thin InSe, further inspiring nanophotonic 2D-material photovoltaic and photocatalytic applications.