Sub-5-nm-period metasurfaces for refractive-index-customized optics

The fixed refractive indices of natural materials constrain the versatility of optical metasurfaces. Here, we introduce sub-5-nm-period nanohole arrays in monolayer MoS₂, where edge-induced defect states reshape the excitonic optical constants. Combining GW-BSE many-body calculations with full-wave simulations reveals that these modified constants in a reflective metasurface configuration govern Fano-type interference between a grating-coupled hybrid resonance and the cavity background, tuning the response from resonant absorption enhancement to interference-dominated suppression. These findings establish few-nanometer defect engineering as a material-level design parameter for tailoring the optical response of metasurfaces.