Ultra‐broadband Epsilon‐Near‐Zero Ultrathin Metafilms Assembled by 2D Nanosheets Overcoming Size Limitation in Metamaterials

ABSTRACT Broadband epsilon‐near‐zero (ENZ) materials are crucial for 6G (sixth generation mobile networks) signal stability, biochemical sensor accuracy, and intelligent weapon systems. Here, the ultrathin ( d ∼10 µm) 2D metafilms achieving low‐frequency ultra‐broadband ENZ (10 kHz–1 MHz, d / λ ∼10 −10 ) are constructed via the self‐assembly of nanosheets (MXene and graphene oxide) and interface engineering. High‐resistance interfaces and wrinkles can block free carriers, suppressing long‐range plasma and Drude‐type negative dielectric response, while these carriers tend to accumulate locally at the interfaces and enhance Debye‐type positive dielectric response. These two pathways achieve the ultra‐broadband ENZ behavior via the synergistic cancellation effect between these two responses with comparable intensity and dispersion characteristics. The ENZ (|ε′|<1) with a 100‐fold ultrabroad bandwidth (10 kHz–1 MHz) is obtained, 10 kHz of ENZ also updates the low‐frequency limit of ENZ in materials. Besides, the thickness of 10 µm is achieved in metafilms, a smallest d / λ value (∼10 −10 ), overcoming the size limitation of ENZ media. The effectiveness of the ultra‐broadband ENZ is verified in electromagnetic tunneling devices, where metafilms can replace complex artificial arrays. This work establishes a new material‐genesis strategy for ultra‐broadband ENZ rather than artificial metamaterial arrays, easily applicable across the entire electromagnetic spectra.