Substrate Effect on Plasmonic Cube Dimers: Reversal of Optical Binding Force Induced by Strong Fano Resonance

TL;DR

This study investigates how substrates influence Fano resonance and optical binding force reversal in plasmonic cube dimers, revealing substrate-dependent effects and stronger coupling on plasmonic substrates.

Contribution

It demonstrates substrate-induced reversal of optical binding forces in plasmonic cube dimers, highlighting the role of strong Fano resonance and substrate coupling, with relaxed parameter sensitivity.

Findings

Reversal occurs only on plasmonic substrates with strong Fano resonance.

Stronger coupling and substrate current enhancement observed during resonance.

Parameter relaxation makes experimental verification more feasible.

Abstract

The behavior of Fano resonance and the reversal of near field optical binding force of dimers over different substrates have not been studied so far. In this work, we observe that if the closely located plasmonic cube homodimers over glass or high permittivity dielectric substrate are illuminated with plane wave polarized parallel to dimer axis, no reversal of optical binding force occurs. But if we apply the same set-up over a plasmonic substrate, stable Fano resonance occurs along with the reversal of near field binding force. It is observed that during such Fano resonance stronger coupling occurs between the dimers and plasmonic substrate along with the strong enhancement of the substrate current. Such near field binding force reversals of plasmonic cube dimers have been explained based on the observed unusual behavior of optical Lorentz force during the induced stronger Fano resonance and the dipole-dipole resonance. Although previously reported reversals of near field optical binding forces were highly sensitive to particle size/shape (i.e. for heterodimers) and inter-particle distance, our configuration provides much relaxation of those parameters and hence should be verified experimentally with simpler experimental set-ups.