Perfect Extinction of Terahertz Waves in Monolayer Graphene over 2‐nm‐Wide Metallic Apertures

High carrier mobility and tunability in graphene enable fundamental studies for plasmonics and various applications. Despite its versatility, however, single‐layer graphene (SLG) suffers from poor coupling efficiency to electromagnetic waves, presenting a major challenge for photonic applications. Compared with visible or infrared radiation, terahertz (THz) waves exhibit higher absorption in SLG due to Drude‐like intraband transitions, but the wavelength‐to‐SLG size mismatch becomes even more dramatic. Here, we experimentally demonstrate 99% extinction of THz wave transmission when SLG covers the openings of 2‐nm‐wide (≈λ/1 000 000) slits through a metal film. By resonantly coupling THz waves through annular nanogaps, the extremely localized fields lead to near‐perfect extinction and strong absorption in SLG. Atomic‐layer lithography is used to produce these nanometer‐wide, millimeter‐long gaps over an entire 4‐in. wafer. Furthermore, by integrating these devices with an ionic liquid, enhanced intraband absorption in the SLG leads to 80% modulation of THz waves with an operational voltage as low as 1.5 V.