Chiroptical interactions between an achiral T-shaped gold nanoparticle and chiral media in the strong coupling regime

The research on the interactions between plasmon and chiral materials is fundamental to the understanding of chiroptical effects and the designs of chiroptical devices. Some theories have been developed to explain the strong interactions between simple nanoparticles and chiral media, but it is difficult to apply to complicated systems. In this paper, we developed an effective method, which utilizes the chiral constitutive relations and finite element method (FEM) simulation, to investigate strong interactions between arbitrary structure and chiral media. To demonstrate the feasibility of our method, we designed a hybrid system by homogeneously coating a layer of chiral medium on achiral T-shaped gold nanoparticle (TGNP). By calculating the circular dichroism (CD) and absorption spectra of the system, we observed a large mode splitting in the CD/absorption spectra, which indicated the system achieves a strong coupling regime. Furthermore, we discovered that the CD spectra of the system can be decomposed into three curves, which are contributed by the chiral media, TGNP, and the optical chirality (OC) density. The chiroptical response of the achiral TGNP is induced by the chiral media and exhibits a strong anti-crossing behavior. The phenomenon can be explained by using the chiral Poynting’s theorem and FEM. Our research has wide potential applications in chiroptical manipulation and chiral quantum optics. •An effective method is developed to investigate strong chiroptical interactions.•A large mode splitting in the CD/absorption spectra are observed.•The CD spectra of the system can be decomposed into three curves.