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

We revisit spin-orbit coupling ina plasmonic Berry metasurface composed 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.

Automated summary

We study spin-orbit coupling in a plasmonic Berry metasurface made up of rotated nanoapertures, which exhibits a strong far-field polarization response. We introduce a scattering formalism that explains how spin-momentum locking emerges from the unit cell geometry, without the need for global rotation symmetries. By using Mueller polarimetry measurements, we confirm that spin-momentum locking is an approximate symmetry and identify the breakdown of this symmetry due to the elliptical projection of circularly polarized light on the planar surface. We also present a new set of spin-momentum locking rules for the excitation of surface waves.