Intrinsic spin-momentum dynamics of surface electromagnetic waves in complex dispersive system

TL;DR

This paper develops a comprehensive theoretical framework for surface electromagnetic waves in dispersive systems, revealing universal spin-momentum locking properties and uncovering new phenomena like longitudinal spin, with implications for nanodevice design.

Contribution

It introduces four dispersive spin-momentum equations for surface waves, clarifies the locking rules in different materials, and demonstrates the effects in topological photonic lattices.

Findings

Universal spin-momentum locking obeys the right-hand rule in dielectrics and left-hand rule in dispersive metals/magnetic materials.

Discovery of an extraordinary longitudinal spin from polarization ellipticity in purely polarized states.

Engineering of photonic topological lattices demonstrates the practical control of spin-momentum locking.

Abstract

Spin-momentum locking is an intrinsic property of surface electromagnetic fields and its study has led to the discovery of photonic spin lattices and diverse applications. Previously, dispersion was ignored in the spin-momentum locking, giving rise to abnormal phenomena contradictory to the physical realities. Here, we formulate four dispersive spin-momentum equations for surface waves, revealing universally that the transverse spin vector is locked with the momentum. The locking property obeys the right-hand rule in the dielectric but the left-hand rule in the dispersive metal/magnetic materials. In addition to the dispersion, the structural features can affect the spin-momentum locking significantly. Remarkably, an extraordinary longitudinal spin originating from the coupling polarization ellipticity is uncovered even for the purely polarized state. We further demonstrate the spin-momentum locking properties with diverse photonic topological lattices by engineering the rotating symmetry. The findings open up opportunities for designing robust nanodevices with practical importance in chiral quantum optics.