Capacitive Enhancements of the Chiroptical Response in Plasmonic Helicoids

Chiral plasmonics has been actively pursued since pushing its light-matter interaction to an unnaturally extreme regime. Recently, chirality-encoded metal–insulator–metal (MIM) motifs have promised compelling advantages in advancing chiroptic responses, as they enable a capacitive coupling and its resultant strong electric and magnetic resonances. However, the deterministic control over chiral MIM working at the visible regime is out of reach. Here, large-area MIM resonators are demonstrated using non-lithographically assembled chiral gold nanoparticles (helicoids) and subsequent gold layer deposition, and their boosted chiroptical responses at the visible regime are proven. The thickness of the topcoat Au and the dielectric gap can precisely tune the strength of capacitive coupling. The numerical analyses support that the optimally tuned capacitive coupling in the chiral MIM structure not only strengthens both electric and magnetic dipolar resonances but also makes their spectral positions closer to each other.