Optical twist induced by plasmonic resonance

Harvesting light for optical torque is of significant importance, owing to its ability to rotate nano- or micro-objects. Nevertheless, applying a strong optical torque remains a challenging task: angular momentum must conserve but light is limited. A simple argument shows the tendency for two objects with strong mutual scattering or light exchange to exhibit a conspicuously enhanced optical torque without large extinction or absorption cross section. The torque on each object is almost equal but opposite, which we called optical twist. The effect is quite significant for plasmonic particle cluster, but can also be observed in structures with other morphologies. Such approach exhibits an unprecedentedly large torque to light extinction or absorption ratio, enabling limited light to exert a relatively large torque without severe heating. Our work contributes to the understanding of optical torque and introduces a novel way to manipulate the internal degrees of freedom of a structured particle cluster.