Long-range structural anisotropy governs macroscopic chiroptical response in twisted anodic aluminum oxide membranes

Abstract

We report twist-angle-dependent circular dichroism (CD) in bilayer anodic aluminum oxide (AAO) membranes separated to avoid near-field coupling. While local pore arrangements exhibit sixfold (C6) symmetry, Fourier analysis reveals a hidden twofold (C2) anisotropy in the long-range structure. This anisotropy governs the optical response: CD spectra display a sin(2θ) modulation, and simulations with weak pore ellipticity reproduce the same trend. The results demonstrate that subtle long-range C2 anisotropy, rather than local C6 symmetry, dictates the macroscopic chiroptical behavior. Unlike static designs with embedded asymmetry, our moiré-inspired platform enables reconfigurable chiroptical responses, as the chiroptical state can be continuously adjusted by rotating the relative in-plane angle between the two AAO membranes. These findings highlight the decisive role of structural anisotropy in far-field chirality and suggest opportunities for reconfigurable chiral photonic devices.