Room Temperature Chiral Coupling of Valley Excitons with Spin-Momentum Locked Surface Plasmons

We demonstrate room temperature chiral coupling of valley excitons in a transition metal dichalcogenide monolayer with spin-momentum locked surface plasmons. At the onset of the strong coupling regime, we measure spin-selective excitation of directional flows of polaritons. Operating under such conditions, our platform yields surprisingly robust intervalley contrasts (ca. 40%) and coherence (ca. 5-8%) as opposed to their total absence for the uncoupled valley excitons at room temperature. These results open rich possibilities, easy to implement, in the context of chiral optical networks.