Steering valley-polarized emission of monolayer MoS₂ sandwiched in plasmonic antennas

Monolayer transition metal dichalcogenides have intrinsic spin-valley degrees of freedom, making it appealing to exploit valleytronic and optoelectronic applications at the nanoscale. Here, we demonstrate that a chiral plasmonic antenna consisting of two stacked gold nanorods can modulate strongly valley-polarized photoluminescence (PL) of monolayer MoS₂ in a broad spectral range at room temperature. The valley-polarized PL of the MoS₂ using the antenna can reach up to ~47%, with approximately three orders of PL magnitude enhancement within the plasmonic nanogap. Besides, the K and K' valleys under opposite circularly polarized light excitation exhibit different emission intensities and directivities in the far field, which can be attributed to the modulation of the valley-dependent excitons by the chiral antenna in both the excitation and emission processes. The distinct features of the ultracompact hybrid suggest potential applications for valleytronic and photonic devices, chiral quantum optics, and high-sensitivity detection.