The chiroptical properties of plasmonic dimer metamaterials based on the extended Born-Kuhn model

Plasmonic dimer metamaterials have been widely utilized in the study of chiral nanophotonics due to their special chiroptical properties. The chiroptical properties of simple rod-like dimer metamaterials can be intuitively described by the Born-Kuhn (BK) model, in which the coupling parameter between oscillators is commonly used as a constant. However, the BK model is limited for complex dimer metamaterials because the behavior of the oscillators is constrained by the geometry of the structure. In this paper, inspired by equivalent LC-coupled circuits, we develop the BK model to predict the chiroptical properties of the split-ring resonator (SRR) dimer metamaterials, where the coupling of oscillators depends on both the twist angle of the SRR dimers and the frequency of the incident light. Using the extended BK model, we predict that there exists a special twist angle, which will cause the chirality of the SRR dimer metamaterials to reverse. More importantly, in such specific spatial configurations, the SRR dimer metamaterials with rectangular slits not only retain the enhancement of the chiral near-field, but also limit the chiroptical far-field response because the interactions of electricity and magnetism cancel each other out. In addition, combined with simulation calculations, we find that the rectangular SRR dimer metamaterials have strong robustness within a certain range of structural regulation. Our work will be helpful for the design and optimization of optical logic elements, chiral sensor components, and coding devices.