Coherent Polaritons in WSe₂-Monolayer-Sandwiched Au-Nanodisk-on-Mirror Structures

Owing to their direct bandgap and spin-valley locking in the visible to near-infrared region, transition metal dichalcogenide monolayers have emerged as promising candidates for next-generation atomically thin optoelectronics. The locking of the electron spin to different valleys offers a valley degree of freedom for information encoding. Nevertheless, the ability to address valley coherence is an important precondition for achieving the quantum manipulation of the valley index. Current access and control of coherent valley information typically relies on the use of high-quality distributed Bragg reflectors and extreme conditions involving an operating temperature of ∼4 K and an applied magnetic field up to 9 T, which is far from the demands of quantum optics and practical optoelectronic applications. In this work, we demonstrate valley coherence under ambient conditions within a sub-145 nm wide area through strong plasmon-exciton coupling featured by distinct Rabi splitting in the photoluminescence spectra. These observations provide insights into strong plasmon-exciton coupling and practical valleytronics.