Microscopic analysis of spin-momentum locking on a geometric phase metasurface

TL;DR

This paper provides a microscopic analysis of spin-momentum locking in a plasmonic Berry metasurface, revealing how geometry influences polarization responses and identifying conditions where symmetry breaks down.

Contribution

It introduces a scattering formalism that explains spin-momentum locking from unit cell geometry without relying on global symmetries.

Findings

Spin-momentum locking is an approximate symmetry confirmed by Mueller polarimetry.

Symmetry breakdown occurs due to elliptical projection of circular polarization.

New spin-momentum locking rules are proposed for surface wave excitation.

Abstract

We revisit spin-orbit coupling in a plasmonic Berry metasurface comprised of rotated nanoapertures, which is known to imprint a robust far-field polarization response. We present a scattering formalism that shows how that spin-momentum locking emerges from the geometry of the unit cell without requiring global rotation symmetries. We find and confirm with Mueller polarimetry measurements that spin-momentum locking is an approximate symmetry. The symmetry breakdown is ascribed to the elliptical projection of circularly polarized light into the planar surface. This breakdown is maximal when surface waves are excited, and a new set of spin-momentum locking rules is presented for this case.