Transverse Chiral Optical Forces by Chiral Surface Plasmon Polaritons

TL;DR

This paper explores how surface plasmon polaritons exhibit transverse spin and Belinfante momentum, leading to chiral optical forces that could enable separation of biomolecules based on chirality.

Contribution

It demonstrates, both analytically and numerically, the existence of transverse chiral forces generated by locally excited surface plasmon polaritons, a novel physical phenomenon.

Findings

Transverse spin angular momentum and Belinfante momentum are present in surface plasmon polaritons.

Transverse chiral forces act oppositely on chiral objects of different handedness.

The magnitude of these forces is comparable to traditional optical forces.

Abstract

Recently the new concepts of transverse spin angular momentum and Belinfante spin momentum of evanescent waves have drawn considerable attention. Here, we investigate these novel physical properties of electromagnetic fields in the context of locally excited surface plasmon polaritons. We demonstrate, both analytically and numerically, that locally excited surface plasmon polaritons possess transverse spin angular momentum and Belinfante momentum with rich and non-trivial characteristics. We also show that the transverse spin angular momentum of locally excited surface plasmon polaritons leads to the emergence of transverse chiral forces in opposite directions for chiral objects of different handedness. The magnitude of such a transverse force is comparable to the optical gradient force and scattering forces. This finding may pave the way for realization of optical separation of chiral biomolecules.