Plasmonic Cube Tetramers over Substrates: Reversal of Binding Force as the Effect of Fano Resonance and Light Polarization

Near-field optical binding force is an emerging new topic in the field of optical manipulation and plasmonics. However, so far, all the studies of near-field binding force and its counterintuitive reversal are only restricted to dimer sets. In this work, we have studied extensively the idea of near-field optical binding force and associated Lorentz force dynamics for more than two objects, such as plasmonic tetramers over different substrates. We have demonstrated that if closely positioned plasmonic cube tetramers are placed only over the plasmonic substrate and the circularly polarized light is impinged over them, all-optical control between their mutual attraction and repulsion is possible because of strong Fano resonance. In addition, the polarization state of light controls the shifting of the extinction spectra and the binding force reversal wavelength, making such nanostructures ideal for the polarization-dependent optical switching device. The high magnitude of attractive and repulsive binding forces has been obtained at the dark and bright resonant modes, respectively, because of strong induced currents in the plasmonic substrate. Because of its simple arrangement, our proposed tetramer configuration may open a novel route for all-optical particle clustering, aggregation, and crystallization, which can be verified by the simple experimental setup.