Plasmonic nanoantenna-dielectric nanocavity hybrids for ultrahigh local electric field enhancement.

A dielectric nanostructure with a high refractive index can exhibit strong optical resonances with considerable electric field enhancement around the entire structure volume. Here we show theoretically that a dielectric structure with this feature can boost the local electric field of a small plasmonic nanoantenna placed nearby. We construct a hybrid system of a plasmonic nanoantenna and a dielectric nanocavity, where the nanocavity is a concentric disk-ring structure with a lossless material n = 3.3 and the nanoantenna is a gold nanorod dimer. The resonant electric field enhancement at the gap center of the antenna in the hybrid structure reaches more than one order of magnitude higher than that of the individual antenna. The dielectric structure plays two roles in the hybrid system, namely the amplified excitation field and an environment causing the redshift of the antenna resonance. The hybrid configuration is applicable to the cases with various geometries and different materials of the hybrid system. Our results can find applications in enhanced nanoscale light-matter interactions such as surface-enhanced Raman scattering, nonlinear optics, and plasmon-exciton couplings.