Negative optical torque in spin-dependent 2D chiral nanomotor due to dipolar scattering

Abstract

We numerically studied the spin-dependent optical torque on a 2D chiral plasmonic nanomotor excited by circularly polarized lights. An interesting phenomenon of so-called negative optical torque is demonstrated on condition that the scattering optical torque is opposite to and larger than absorption optical torque under a plasmonic resonance of dipolar mode. Moreover, the calculated optical torque, exerted on the nanomotor, is monotonically tunable depending on the ellipticity of light. It is theoretically estimated that the spin-dependent rotation frequency can be modulated from about 3.56 kHz to 8.91 kHz under incident intensity of 1mW∕μm2. Our results demonstrate a counterintuitive rotation phenomenon on light-driven 2D chiral nanomotor, and open a manipulation avenue to control optically-induced torque via absorption and/or scattering of light by 2D chiral plasmonic meta-atom.