Visualizing Nanoscale Valley Polarization in Transition Metal Dichalcogenides Using Tip-Enhanced Circularly Polarized Photoluminescence Imaging

Mapping the spatial distribution of valley polarization at the nanoscale is essential for understanding the influence of local inhomogeneities to the performance of transition metal dichalcogenide (TMD) valleytronic devices but remains challenging due to the spatial resolution limits of conventional optical techniques. Herein, we introduce tip-enhanced circularly polarized photoluminescence (TECPPL) imaging, enabling the simultaneous mapping of exciton emission intensity and valley polarization. We investigate a monolayer (1L) MoS₂/WS₂ heterojunction (HJ) and observe pronounced near-field (NF) photoluminescence (PL) enhancement under both σ⁺σ⁺ and σ⁺σ^- polarization configurations. A NF circular polarization degree (P_c) of 0.67 is achieved, representing a 4-fold increase over the far-field (FF) measurement. The high local signal enhancement enables direct visualization of spatial variations in both the PL intensity and P_c with a spatial resolution of ∼20 nm. Our results establish TECPPL as a powerful nanospectroscopic tool and offer new insights into the spatially resolved valleytronic behavior of TMD heterostructures.