Selectively Depopulating Valley-Polarized Excitons in Monolayer MoS₂by Local Chirality in Single Plasmonic Nanocavity

Transition metal dichalcogenides, whose valley degrees of freedom are characterized by the degree of circular polarization (DCP) of the photoluminescence, draw broad interests due to their potential applications in information storage and processing. However, this DCP is usually low at room temperature due to the phonon-assisted intervalley scattering, severely degrading the fidelity of the valley-stored signals. Therefore, achieving high DCP at room temperature is vital for valley-encoded nanophotonic devices. In this work, we demonstrate a high DCP of 48.7% at room temperature by embedding monolayer MoS2 into a compact plasmonic nanocavity. Such a high DCP is proven to originate from the prominent chiral Purcell effect owing to the degeneracy-lifted circularly polarized local density of states in the nanocavity. In addition, the DCP can be further manipulated by an in situ plasmon-scanned technique. This highly compact system provides possibilities for developing versatile valley-encoded light-emitting devices at room temperature.