Routing the Plasmon-Brightened Emission of Dark Excitons in Monolayer WSe₂ at Room Temperature.

Abstract

Dark excitons in transition-metal dichalcogenides, distinguished by spin-forbidden transitions and long lifetimes, are crucial to quantum science and valleytronics. However, their inherent optical inactivity and the limitations of conventional brightening approaches (requirements of cryostats or external magnetic/electric fields) hinder practical applications. Here, we present an innovative nanoantenna pair platform that overcomes these challenges through dual functionality: (i) <i>in situ</i> activation of dark excitons via a nanocube-on-mirror nanocavity that resonantly couples the excitons' out-of-plane dipole to a vertically enhanced electric field and (ii) propagative control of exciton emission enabled by surface plasmon polariton waveguiding between spatially separated "receiving" and "transmitting" antennas. This architecture uniquely reduces local heating effects and background noise inherent in traditional plasmonic systems while achieving <i>in situ</i> brightening and remote routing of dark exciton emission at room temperature. Our work establishes a nanoscale paradigm for integrating dark excitons into quantum photonic circuits and on-chip optoelectronic devices.