Abstract
Flatbands have long been a key topic in condensed-matter physics and photonics, which have significant impact on both fundamental physics and applications, including magic-angle physics, diffractionless wave propagation, and enhanced photon-electron interaction. However, the flatband systems usually rely on strict structural parameters or complex material system, such as twisted graphene right at magic angle and exquisitely designed photonic crystals, which restricts more extensive research of flatband. On the other hand, polaritons in van der Waals materials have attracted great attention due to high tunability, abundant anisotropy, and strong electromagnetic confinement and enhancement, which may bring new opportunities for flatband research.
In theory, we research a kind of surface polaritons in Van der Waals materials and observe surface flatband near the interface between the materials and the air, where the polaritons shows diffractionless propagation. As the surface polaritons is sensitive to surrounding media, the flatband is tunable and can be realized in a broad frequency range. What’s more, by changing the surrounding media, the surface mode dispersion can enter bulk state zone and become surface BIC.
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