Giant terahertz pulling force within an evanescent field induced by asymmetric wave coupling into radiative and bound modes.

Manipulation of nano-scale objects by engineering the electromagnetic waves in the environment medium is pivotal for several particle handling techniques using optical resonators, waveguiding, and plasmonic devices. In this Letter, we theoretically demonstrate the possibility of engineering a compact and tunable plasmon-based terahertz (THz) tweezer using a graphene monolayer that is deposited on a high-index dielectric substrate. When a nanoparticle located in a vacuum in the vicinity of the graphene monolayer is illuminated under total internal reflection, as light is launched from the substrate, such a device is shown to be capable of inducing an enhanced rotating dipole in the nanoparticle thus enabling asymmetric, directional near-field coupling into the graphene plasmon mode and the radiative modes in the substrate. As a result of the total momentum conservation, the net force exerted on the particle points in a direction opposite to the pushing scattering force of the exciting evanescent field. Our results can contribute to novel realizations of photonic devices based on polarization-dependent interactions between nanoparticles and electromagnetic mode fields.