Dipolar Resonance Enhancement and Magnetic Resonance in Cross-Coupled Bow-Tie Nanoantenna Array by Plasmonic Cavity

We experimentally demonstrate a simple approach for surface current engineering in a cross-coupled bow-tie nanoantenna by inserting a plasmonic cavity that simultaneously offers (i) improved Fano-like dipolar resonance contrast, (ii) electrically induced magnetic resonance, and (iii) enhanced sensitivity. By introducing a small geometric perturbation, we propose two physical parameters, offset (f) and split gap (s), for strong modulation of resonance location and intensity. We report at least 3.75-fold better dipolar resonance compared with the conventional design and demonstrate a unique mechanism for exciting magnetic plasmonic resonance. Finally, we obtain a large wavelength shift of 777.5 and 904 nm per refractive index unit (RIU) with a thin PMMA coating (110 nm) for the dipolar resonance and magnetic resonance, respectively. Numerical study indicates the potential of the proposed bow-tie nanoantenna array structure with a self-similar plasmonic cavity (SSP BNA) for sensitive recording of binding events of molecules such as DNA by reestablishing conduction current and providing “on” and “off” states. The high-density plasmonic antenna array structure will be promising for engineering applications in optical magnetism, magnetoplasmonics, optical trapping, and massively parallel ultrasensitive differential detection of molecular fingerprints.