Chalcogenide phase‐change materials (PCMs) have offered an appealing material solution by acting as a switchable dielectric layer to tune the electromagnetic properties of terahertz metamaterials and metasurfaces. Here, this work demonstrates large‐scale and lithography‐free manufacturing of all‐PCM terahertz metasurfaces based on direct laser switching of crystalline micro‐domains in a thin film with high switching ratio of the emerging plasmonic PCM, In3SbTe2 (IST). The fabricated high‐quality IST metasurfaces achieve efficient plasmonic resonances and a large modulation depth with ultrafast response (full width at half maxima of the modulation time ≈1.6 ps) in a deep‐subwavelength switching volume. For the dynamic evolution of terahertz resonance modes, theoretical modeling reveals a delicate interplay between amorphous and crystalline IST due to the bonding‐structure‐induced different carrier lifetimes and spatially localized electric fields. These studies open new avenues for realizing all‐PCM terahertz ultrafast nanophotonics.
Approaches to generate and manipulate Cherenkov radiation (CR) are challenging yet meaningful. Optical topological transition (OTT) in novel materials and metamaterials is also promising for modern photonics. We study the OTT of CR in graphene-based hyperbolic metamaterials (GHMs) for the first time. In GHMs, conventional and hyperbolic CR can be switched when crossing the topological transition frequency. This frequency can be altered by metamaterial components and external optical elements. For instance, external ultrafast optical pumps cause an ultrafast OTT from the elliptical to the hyperbolic state. Then, hyperbolic CR can be excited by low-energy electrons by leveraging the excellent photothermal properties of graphene. Hyperbolic CR vanishes when the GHM returns to its original state. Furthermore, graphene nonlocality occurs when the electron velocity is low enough, corresponding to a large wave vector. Concretely, when the electron velocity approaches the Fermi velocity of graphene, a nonlocality-induced OTT modifies the plasmonic properties of the GHM and brings a new lower velocity threshold of hyperbolic CR. Therefore, hyperbolic CR can only be induced in a limited velocity range. These findings pave the way for understanding CR properties in active plasmonic metamaterials and may be applied to complex photonic and polaritonic systems.
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