Toroidal-dipole-resonance-induced reversal of the lateral optical force on plasmonic nanoparticle clusters

Based on full-wave simulations, we demonstrate that a spectrally isolated toroidal dipole resonance can induce a direction reversal of the lateral optical force (OF) acting on plasmonic nanoparticle clusters illuminated by a linearly polarized plane-wave optical field. The spatial profiles of the electric and magnetic fields, as well as the individual radiation powers from different multipoles on the clusters, are presented to establish the association of the lateral OF reversal with the toroidal dipole resonance. The angular distribution of far-field scattered irradiance is exhibited to elucidate its physical origin. The phenomenon suggests an alternative way of optically manipulating the plasmonic nanoparticle aggregates that support toroidal moments and clusters involving toroidal molecular structures.