Metal–Dielectric Hybrid Dimer Nanoantenna: Coupling between Surface Plasmons and Dielectric Resonances for Fluorescence Enhancement

Abstract

Dimers made of noble metal particles possess extraordinary field enhancements but suffer from large dissipation, whereas low-loss dielectric dimers are limited by relatively weak optical confinement. Hybrid systems could take advantages from both worlds. In this contribution, we study the mode coupling in a hybrid dimer with rigorous dipole–dipole interaction theory and explore its potential in fluorescence enhancement. We first discovered that the direct coupling between metal surface–plasmon resonance and dielectric electric–dipole mode creates a hybridized mode due to the strong electric–electric dipole–dipole interaction between the constituent nanoparticles, whereas the dielectric magnetic–dipole mode can only indirectly couple to the plasmons on the basis of the induced electric–magnetic dipole–dipole interaction. When an electric/magnetic quantum emitter couples to the hybrid dimer, the emitter selectively excites the electric/magnetic (magnetic/electric) resonant modes of the dimer for emitter orientation parallel (perpendicular) to the dimer axis. Our study shows that the hybrid dimer simultaneously possesses high field enhancement and low-loss features, which demonstrates a fluorescence excitation rate 40% higher than that of the pure dielectric dimer and an average quantum yield 30% higher than that of the pure metallic dimer. On top of that, the unique asymmetrical structure of the hybrid dimer directs 20% more radiation toward the dielectric side, hence improving the directivity of the dimer as an antenna.