Topological Polaritonic Metamaterials Realized in Bulk Transition Metal Dichalcogenide Crystals

Due to the enhanced nature of the interactions of light with quantum excitations, topological polaritonic (TP) systems form a unique platform that offers on‐chip control over half‐light, half‐matter excitations via synthetic degrees of freedom. Among other polaritonic platforms, van der Waals materials (vdW) have recently attracted significant interest due to the relative simplicity of their integration into topological photonic structures. Several TP insulators based on vdW materials have been demonstrated; however, they rely on hybrid structures with nanopatterned dielectric substrates, which limit the strength of light‐matter interactions. Here, a monolithic all‐vdW TP insulator based on bulk crystals of transition metal dichalcogenide WS 2 is designed and experimentally realized. Due to their high refractive index and the presence of exciton modes, these nanomaterials prove to be excellent platforms for TPs, offering both excellent confinement and strong light‐matter interactions in monolithic structures. The emergence of TP boundary modes is confirmed by Fourier and real‐space imaging, and a dramatic reduction in dissipation is observed at cryogenic temperatures. The proposed monolithic all‐vdW topological insulators, which are characterized by extreme confinement of optical fields and moderate losses, can serve as an alternative to silicon photonics‐based systems in the quest for the development of polaritonic quantum technologies.