Twist-engineered acoustic plasmon nanocavities enable deep-nanoscale terahertz molecular fingerprinting

Abstract Field-enhanced terahertz spectroscopy serves as a powerful analytical tool for biochemical sensing, materials characterization, and medical diagnostics, where detection sensitivity fundamentally depends on electric field enhancement and confinement. However, the severe scale mismatch between long terahertz wavelengths (on the order of 100 $$\upmu$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>μ</mml:mi> </mml:math> m) and nanoscale analytes (typically &lt; 10 nm) imposes critical limitations on conventional far-field techniques. Here, we present a breakthrough sensing approach utilizing twisted double-layer graphene plasmonic metasurfaces (t-DL-GPMs) with nanometric dielectric spacers. Our investigations reveal that these t-DL-GPMs support strongly confined acoustic plasmon nanocavity modes featuring extraordinary field enhancement and deep subwavelength field concentration, along with an extremely small mode volume (10 −13 λ 0 3 ). Compared to single-layer and untwisted double-layer graphene configurations, the twisted architecture demonstrates dramatically improved sensing performance, with figures of merit enhanced by factors of 22 and 48, respectively. Most significantly, the platform enables clear identification of terahertz vibrational fingerprints from molecular layers as thin as 1 nm. This work not only opens novel avenues for nanoscale terahertz detection, pushing the THz sensing into unprecedented deep-nano level, but also establishes a versatile foundation for exploring extreme light-matter interactions and developing advanced terahertz photonic devices.