The Mechanism of Chirality in Plasmonic Structures: Asymmetric Resonance Modes

Abstract

This study presents a theoretical framework for understanding the mechanism of chirality generation and circular dichroism (CD) in chiral nanostructures, with a particular focus on the role of asymmetric plasmon resonance mode distributions. Although previous studies have linked chiroptical properties to resonance differences, the specific nature and origin of these differences have not been fully elucidated. Here, we provide a more detailed explanation by quantitatively analyzing the asymmetric electric-field components arising from mode asymmetry. Specifically, we examine the near-field symmetry of individual nanorods and corner-stacked coupled structures (CSCS). The results demonstrate that chirality arises from asymmetric electric-field distributions, which give rise to distinct phase and amplitude responses of the electromagnetic fields in the composite structure under right-handed circularly polarized (RCP) and left-handed circularly polarized (LCP) illumination. The absorption and CD spectra, which exhibit distinct features around $910\,\mathrm{nm}$, support this mechanism and provide valuable insights into the design of chiroptical materials. The proposed mechanism is not restricted to a specific chiral structure or resonance and offers a broader explanation for the generation of circular dichroism.