Dark excitons are electron hole pairs that are dark because their spin or momentum configuration prevents them from easily emitting light. Dark excitons have long lifetimes and can be useful for quantum technology information storage units, but they are challenging to observe. Unlike bright excitons which easily emit light, dark excitons require extra energy or a spin flip to become visible. In monolayers of transition metal dichalcogenides (TMDs) the strong Coulomb interaction arising from weak dielectric screening and extreme quantum confinement results in prominent exciton states. Therefore, dark excitons in atomically thin materials provide an exciting platform for quantum and nanophotonic applications.
Recently, new work has been presented which utilizes a heterostructure consisting of optimized plasmonic metal nanocubes coupled to a tungsten diselenide monolayer encapsulated between thin hexagonal boron nitride layers to unveil a new family of dark excitons. The emission of these dark excitons is 2,700 times stronger than bright excitons, yielding a striking enhancement factor of 30,000. Furthermore, they are selectively activated by controlling the Fermi level via electric doping. These dark excitons also have narrow linewidths, long lifetime, and efficient electrical and magnetic modulation.
The novel work was reported by Jiamin Quan, Michele Cotrufo, Saroj Chand, Xuefeng Jiang, Zhida Liu, Enrique Alejandro Mejia IV, Wei Wang, Takashi Taniguchi, Kenji Watanabe, Gabriele Grosso, Xiaoqin Li, and Andrea Alù in a collaborative effort from Advanced Science Research Center, GC/CUNY, The City University of New York, The University of Texas at Austin, and the National Institute for Materials Science in Tsukuba, Japan.
The work was performed in part using both an STS-Elionix ELS-G100 and ELS-G50 electron beam lithography system at the Advanced Science Research Center, GC/CUNY facility.
For more information see https://doi.org/10.1038/s41566-025-01788-w
Image (courtesy Jiamin Quan): Scanning electron microscope image of nanocube patterns ranging from 70 nm to 200 nm square made by an STS-Elionix ELS-G100 electron beam lithography system.