Multiscale Chirality in Moiré Metasurfaces Revealed by Terahertz Circular Dichroism Spectroscopic Imaging

Abstract

Terahertz circular dichroism (THz-CD) spectroscopy provides unique access to low-energy chiral interactions between circularly polarized THz light and multiscale chirality in materials. Yet it has remained unclear whether the THz band can function as a practical, high-fidelity probe that produces visualization of spatial distribution of such interactions. Here, we establish that it can by introducing a frequency-tunable THz-CD spectroscopic imaging platform operating across 3–6 THz with narrow spectral bandwidth, circularly polarized excitation, and two-dimensional readout. Using twisted-layer moiré metasurfaces (TMMSs) as a top-down, reconfigurable model system that allows deterministic design and control of chirality─in contrast to bottom-up chiral media such as biomolecules, whose handedness is constrained by biochemical stability─we spatially resolve chiral responses that elude spatially averaged spectra: the dissymmetry (g-factor) inverts sign between topological singularities within a single planar architecture and reverses with the twist handedness, whereas scale moiré counterparts remain achiral. We formulate complementary indicators for local displacement asymmetry and macroscopic rotational geometry and show that only their combined action reproduces the measured 2D images, thereby providing experimental validation of a multiscale description in the THz regime. Beyond this platform, our results position spatial THz-CD imaging (3–6 THz) as a practical tool for site-specific chiral metrology in metasurfaces, soft-phonon materials, and biomolecular assemblies.