Electromagnetic Interaction in Plasmonic Artificial Molecules

Plasmonic hotspots located in the nanogaps of infrared optical antennas are mapped in the near-field. The enhanced evanescent fields are imaged as a function of excitation wavelength, polarization, particle length, gap size, and tip material. The near-field resonance behavior of antennas composed of rods, ``bowtie'' and ``fourtie'' infrared antenna structures reveals that field enhancement strongly depends on the particle length and interparticle gaps. In rod antenna-field imaging using scattering probes, the probe tip can be considered as a load in the gap of the antenna, and the antenna response to tips can be directly understood by using nanocircuit theory. Experimental results are in agreement with finite-difference time-domain (FDTD) simulations.