Valley-Dependent Emission Patterns Enabled by Plasmonic Nanoantennas

Selective control of the emission pattern of valley-polarized excitons in monolayer transition metal dichalcogenides is essential for advancing valleytronic, quantum information, and optoelectronic devices. Although substantial progress has been made in directionally routing photoluminescence from these materials, key challenges persist: specifically, establishing how observed routing effects relate to the degree of valley polarization and distinguishing genuine valley-dependent routing from spin-momentum coupling, an optical scattering effect unrelated to the emitter. In this work, we address these challenges by experimentally and numerically demonstrating a direct link between excitonic valley polarization and the resulting farfield emission pattern, enabling quantitative evaluation of valley-selective emission routing. We report valley-dependent manipulation of the angular emission pattern of monolayer tungsten diselenide using gold nanobar dimer antennas at cryogenic temperatures. By probing the emission under opposite circularly polarized excitation, we observe a valley-selective asymmetry in the photoluminescence circular dichroism of 2%. These measurements are supported by a reciprocity-based numerical framework that enables modeling of valley-selective emission in periodic systems. Our calculations further reveal that the observed valley-dependent directionality is a symmetry-protected property of the nanoantenna array arising from its extrinsic chirality at oblique emission angles, and that it can be substantially enhanced by tailoring the emitter distribution. Together, these results establish our nanoantenna platform as a robust route toward valleytronic signal processing.