Near-field enhancement of light by higher-order multipole excitations in a metal nanodisc trimer

Near-field enhancement of light by dipole excitations in plasmonic nanoparticles plays an important role in many applications of optical nanotechnology, including solar cells, plasmonic sensors, and nonlinear optical devices. Recently, we have shown that a seemingly weak octupole resonance in a pair of metal nanospheres can provide a higher near-field enhancement than the dipole resonance. Being motivated by this discovery, we now design a plasmonic nanodisc trimer that supports hybridized higher-order excitations and simultaneously suppresses the dipole excitation. We show that, under these conditions, the near-field enhancement can reach a high level, exceeding the value achievable with a corresponding dimer structure. The interference of the electric currents belonging to different multipole moments is found to play an important role in the enhancement. We believe that arrays of similar metal nanostructures can be designed to enhance optical fields via higher-order resonances for many applications, e.g., in nonlinear optics and optical sensing based on surface-enhanced fluorescence or Raman scattering.