Breaking the symmetry for giant circular dichroism and near-perfect absorption in chiral magnetoplasmonic systems by indirect nearfield coupling

Abstract Adaptive, polarization-selective perfect absorbers are pivotal for next-generation chiral photonics, but conventional metal–insulator–metal (MIM) platforms suffer from immutable resonance positions and limited chiro-optical contrast. Replacing the dielectric spacer of MIM absorbers with magneto-optically active BIG film, here we introduce a metal–magnetic–metal (MMM) chiral absorber that reconfigures both the resonance wavelength and circular-dichroic (CD) strength. Leveraging the magneto-optic Faraday effect and structurally induced plasmonic chirality, the bottom Au film acts as a phase tunable plasmonic mirror which derives the dual-band, near-unity absorption (>90%) and strong CD (>60%) within a 900–1500 nm window, while preserving sub-10 nm linewidths. Rigorous electromagnetic analysis reveals that the CD arises from the indirect nearfield coupling between the upper plasmonic nanostructure and the lower metallic film, visualized through surface-charge and local-field maps. Beyond absorption, the identical architecture functions in magneto-chiral sensing, and can detect minute variations in external magnetic fields. These results establish MMM metamaterials as a versatile route towards magnetically tunable, multifunctional chiral devices for polarimetric imaging, enantioselective sensing and on-chip optical isolators.