Chiral Surface Wave propagation with Anomalous Spin-momentum Locking

TL;DR

This paper introduces chiral surface waves with dual transverse spins, enabling enhanced control of wave propagation and spin-orbit interaction through novel metasurface design, advancing applications in spintronics and polarization optics.

Contribution

It presents a new type of surface wave with two transverse spins, one inherent and one design-enforced, demonstrating spin-momentum locking and expanding metasurface capabilities.

Findings

Chiral surface waves possess two locked transverse spins.

Design enables out-of-plane spin via strong coupling and symmetry breaking.

Enhanced control over wave directionality and spin-orbit interaction.

Abstract

The ability to control the directionality of surface waves by manipulating its polarization has been of great significance for applications in spintronics and polarization-based optics. Surface waves with evanescent tails are found to possess an inherent in-plane transverse spin which is dependent on the propagation direction while an out-of-plane transverse spin does not naturally occur for surface waves and requires a specific surface design. Here, we introduce a new type of surface waves called chiral surface wave which has two transverse spins, an in-plane one that is inherent to any surface wave and an out-of-plane spin which is enforced by the design due to strong x-to-y coupling and broken rotational symmetry. The two transverse spins are locked to the momentum. Our study opens a new direction for metasurface designs with enhanced and controlled spin-orbit interaction by adding an extra degree of freedom to control the propagation direction as well as the transverse spin of surface waves.