Integration of 2D Materials in Radial van der Waals Heterostructure Metasurfaces.

Two-dimensional semiconductors, such as monolayer transition metal dichalcogenides (TMD), exhibit strong excitonic transitions at room temperature and offer a platform for exploring light-matter interactions in nanoscale photonic systems. In this work, we demonstrate a compact and polarization-invariant photonic metasurface, fabricated from hexagonal boron-nitride (hBN) and based on radial bound states in the continuum (BIC), which are formed by radially distributed pairs of structurally asymmetric resonators. The metasurface employs multiple symmetry-breaking perturbations to support high-quality (Q) factor resonances within a radial footprint of 4.5 μm - approximately one-sixth of the area of previous hBN BIC metasurface implementations based on large periodic arrays. Compared to these approaches, the radial geometry furthermore achieves sizable Q-factors with a reduced footprint. By integrating the hBN photonic structure with a WS2 monolayer, we observe enhanced photoluminescence when its resonance is spectrally aligned with the exciton resonance, accompanied by signatures of discrete momentum-space patterns that identify the orbital-angular-momentum-carrying ring eigenmodes. These features persist over a wide range of excitation powers and show minimal linewidth broadening, indicating robust and spatially modulated exciton-photon coupling. This work establishes a scalable approach for generating hybrid photonic-excitonic states with momentum-space structure, offering opportunities for exciton localization, valley emission, spatially programmable light-matter interaction in 2D material platforms and compact luminescent devices based on 2D material integrated metasurfaces.