Directional Chiral Exciton Emission via Topological Polarization Singularities in all Van der Waals Metasurfaces.

Monolayer transition metal dichalcogenides (TMDs) with strong exciton effects have enabled diverse light emitting devices, however, their Ångstrom thickness makes it challenging to efficiently manipulate exciton emission by themselves. Although their nanostructured multi-layer counterparts can effectively manipulate optical field at deep subwavelength thickness scale, these indirect band gap multi-layer TMDs are lack of strong luminescence, hindering their applications in light emitting devices. Here, the integration of monolayer TMDs is presented with nanostructured multi-layer TMDs, combining both strong exciton emission and optical manipulation in a single ultra-thin platform. Leveraging the topological polarization singularities in the all van der Waals metasurfaces, chiral exciton emission is experimentally demonstrated whose directionality can be controlled by tailoring metasurface's symmetry. These results provide an approach that can realize exciton emitting devices fully based on 2D materials with controllable polarization and directionality, and may unfold a new avenue for multi-functional 2D semiconductor light sources.