AUTHORS:

Zograf G., Küçüköz B., Polyakov A.Yu., Yankovich A.B., Ranjan A., Bancerek M., Agrawal A.V., Olsson E., Wieczorek W., Antosiewicz T.J. & Shegai T.O.

ABSTRACT:

Dielectric metasurfaces that combine high-index materials with optical nonlinearities are recognized for their potential in quantum and classical nanophotonic applications. However, the fabrication of high-quality metasurfaces poses material-dependent challenges, as their designs are often susceptible to disorder, defects, and scattering losses, mostly occurring at the edges of nanostructured features. Additionally, the choice of the material platforms featuring second-order optical nonlinearities χ⁽²⁾, is limited to broken-inversion symmetry crystals such as GaAs, GaP, LiNbO₃, and various bulk van der Waals materials. Here, we use a combination of top-down lithography and anisotropic wet etching of a specially stacked van der Waals crystal – 3R-MoS₂, which exhibits both a high refractive index and exceptional χ⁽²⁾ nonlinearity, to produce ultrathin (~20–25 nm) metasurfaces with atomically sharp edges, where the etching breaks the in-plane symmetry of the meta-atoms. The broken symmetry manifests as a quasi-boundstate-in-the-continuum, enabling the enhancement of second-harmonic generation of three orders of magnitude at specific wavelengths.

Communications physics, 2025, vol. 8, art. 271, doi: 10.1038/s42005-025-02194-y