Interparticle-Interaction-Mediated Anomalous Acceleration of Nanoparticles under Light-Field with Coupled Orbital and Spin Angular Momentum.

Spin-orbit interaction is a crucial issue in the field of nanoscale physics and chemistry. Here, we theoretically demonstrate that the spin angular momentum (SAM) can accelerate and decelerate the orbital motion of nanoparticles (NPs) via light-induced interparticle interactions by a circularly polarized optical vortex. The Laguerre-Gaussian beam as a conventional optical vortex with orbital angular momentum (OAM) induces the orbital and spinning motion of a trapped object depending on the spatial configuration. On the contrary, it is not clear whether circularly polarized light induces the orbital motion for the particles trapped off-axis. The present study reveals that the interparticle light-induced force due to the SAM enhances or weakens the orbital torque and modulates rotational dynamics depending on the number of NPs, where the rotation speed of NPs in the optical field with both positive SAM and OAM can be 4 times faster than that in the optical field with negative SAM and positive OAM. The obtained results will not only clarify the principle for the control of NPs based on OAM-SAM coupling via light-matter interaction but also contribute to the unconventional laser processing technique for nanostructures with various chiral symmetries.