Spherical Plasmonic Heterodimers: Reversal of Optical Binding Force as the Effect of Symmetry Breaking

TL;DR

This paper investigates how symmetry breaking in spherical plasmonic heterodimers causes reversal of near-field optical binding forces through distinct mechanisms, offering new insights for controlling plasmonic interactions.

Contribution

It reveals that force reversal mechanisms differ for lateral and longitudinal configurations, challenging previous assumptions and providing new methods for force control via symmetry breaking.

Findings

Force reversal depends on symmetry breaking and configuration type.

Longitudinal force reversal can be controlled by light direction and orientation.

Opposes Fano resonance-based explanations, proposing alternative Lorentz force dynamics.

Abstract

The stimulating connection between the reversal of near field plasmonic binding force and the role of symmetry breaking has not been investigated in detail in literature. As both bonding and anti-bonding modes are present in the visible spectra of well-known spherical plasmonic heterodimer sets, binding force reversal is commonly believed to occur for all such heterodimers. But our work suggests a very different proposal. We demonstrate that for the symmetry broken heterodimer configurations: reversal of lateral (for on-axis heterodimers) and longitudinal (for off-axis heterodimers: end-fire and nearly end-fire configurations) near field binding force follow fully distinct mechanisms; i.e. later one on relative orientation and constructive dipole-quadrupole resonance but the former one on light polarization and the induced electric resonance. Interestingly, the reversal of longitudinal near field binding force can be easily controlled just by changing the direction of light propagation or just their relative orientation. Though it is commonly believed that plasmonic forces mostly arise from the surface force and Fano resonance can be a promising way to achieve binding force reversal; our study based on Lorentz force dynamics suggests notably opposite proposals (for both instances) for the case of plasmonic spherical heterodimers. Observations of this article can be very useful for improved sensors, particle clustering and aggregation.