Manipulating the intrinsic light–matter interaction with high- <i>Q</i> resonances in an etch-free van der Waals metasurface

Recent demonstrations of van der Waals (vdW) nanophotonics have opened new, to our knowledge, pathways for manipulating the light–matter interaction in an intrinsic manner, leading to fascinating achievements including tunable magneto-optics, indirect bandgap lasing, and exceptionally enhanced optical nonlinearity. However, the anisotropic atomic lattice structures, chemically active sidewalls, and distinct enthalpies of formation across vdW materials pose challenges in on-demand nano-fabrications, hindering high- Q resonances achieved in arbitrary vdW materials. In this work, we propose an alternative etch-free vdW structure where a layer of nanostructures made of a low-refractive-index (LRI) photoresist is fabricated on top of a vdW layer. Thanks to the reduced scattering loss by LRI nanostructures, the measured Q factor can reach 348 approaching the highest value achieved with TMDC metasurfaces. Based on this platform, room-temperature polaritons are demonstrated in four representative materials, i.e., WS 2 ,MoS 2 ,WSe 2 , and MoSe 2 , through self-hybridization of quasi-bound states in the continuum (BIC) and excitons. An unambiguous anti-crossing behavior is observed in WS 2 and MoSe 2 samples with Rabi-splitting approaching approximately 80 and 72 meV, respectively, significantly surpassing their separate intrinsic excitonic losses. Further, we demonstrate the emission modulation in the phonon-assisted indirect bandgap transition in bulk WS 2 and bright exciton emission in a monolayer MoSe 2 encapsulated between two hBN layers. The polarization-dependent emission enhancement is achieved in both these systems. Our work demonstrates a general strategy in vdW nanophotonics to achieve intrinsic light–matter interaction with high- Q resonances. The etch-free structure shows no preference of material choices and preserves the material integrity, advancing applications in photoelectronic and quantum devices based on arbitrary vdW materials and their heterostructures.