Lateral recoil optical forces on nanoparticles near nonreciprocal surfaces

TL;DR

This paper develops a theoretical framework to analyze lateral recoil forces on nanoparticles near nonreciprocal plasmonic surfaces, revealing dominant forces due to surface plasmon momentum imbalance that can be harnessed for nanoparticle manipulation.

Contribution

It introduces a comprehensive theoretical model for lateral recoil forces near nonreciprocal surfaces and demonstrates their dependence on surface plasmon dispersion and bias, with potential applications in nanoparticle sorting.

Findings

Lateral recoil forces can be significantly larger than other force components.

These forces depend mainly on the nonreciprocal surface plasmon momentum.

Proposed platform can sort nanoparticles by size using drift-biased graphene metasurfaces.

Abstract

We investigate lateral recoil forces exerted on nanoparticles located near plasmonic platforms with in-plane nonreciprocal response. To this purpose, we first develop a comprehensive theoretical framework based on the Lorentz force within the Rayleigh approximation combined with nonreciprocal Green's functions and then derive approximate analytical expressions to model lateral recoil forces, demonstrating their explicit dependence on the dispersion relation of the system and unveiling the mechanisms that govern them. In particular, a dominant lateral recoil force component appears due to the momentum imbalance of nonreciprocal surface plasmons supported by the platform. This force can be orders of magnitude larger than other recoil force components, acts only along or against the direction of the external bias, and is quasi-independent of the direction, polarization, and wavelength of the incident plane wave. Lateral recoil forces are explored using drift-biased graphene metasurfaces, a platform that is also proposed to sort nanoparticles as a function of their size. Nonreciprocal plasmonic systems may enable new venues to trap, bind, and manipulate nanoparticles and to alleviate some of the challenges of conventional optical tweezers.