Chiroptical Evolution of Plasmonic Helicoids Induced by High-Refractive-Index Dielectric Substrates

Chiroptical responses of chiral plasmonic nanoparticles are influenced by their morphology, yet the impact of supporting substrates is significant but not fully understood. In this study, we numerically investigate the effect of high-refractive-index dielectric substrates on the chiroptical response of individual chiral plasmonic nanoparticles. Using Au helicoid as an example, we observe that as the refractive index of the supporting substrate increases, there is a remarkable enhancement in the dissymmetry factor (g-factor), along with an abnormal peak separation between the absorption and scattering g-factor spectra, which is different from typical observations. This unique chiroptical evolution is attributed to the strong plasmon hybridization under circularly polarized in-plane excitation. To validate the universality of these findings, we vary the size and material of the helicoid, confirming the consistent occurrence of this phenomenon. Our findings provide valuable insights into the substrate effect of chiral plasmonic nanoparticles to facilitate their applications in on-chip devices and sensing technologies.