Capacitive Enhancements of the Chiroptical Response in Plasmonic Helicoids

摘要

Chiral plasmonics has been actively pursued since pushing its light-matterinteraction to an unnaturally extreme regime. Recently, chirality-encodedmetal–insulator–metal (MIM) motifs have promised compelling advantagesin advancing chiroptic responses, as they enable a capacitive coupling and itsresultant strong electric and magnetic resonances. However, the deterministiccontrol over chiral MIM working at the visible regime is out of reach. Here,large-area MIM resonators are demonstrated using non-lithographicallyassembled chiral gold nanoparticles (helicoids) and subsequent gold layerdeposition, and their boosted chiroptical responses at the visible regime areproven. The thickness of the topcoat Au and the dielectric gap can preciselytune the strength of capacitive coupling. The numerical analyses support thatthe optimally tuned capacitive coupling in the chiral MIM structure not onlystrengthens both electric and magnetic dipolar resonances but also makestheir spectral positions closer to each other.