Spin-Split Dispersion of Leaky Surface plasmons in Inversion- Symmetric System

TL;DR

This paper demonstrates a novel spin-split dispersion of leaky surface plasmons in an inversion-symmetric system, revealing spin-momentum locking and polarization effects through a unique optical measurement setup.

Contribution

It introduces a new spin-split dispersion phenomenon in symmetric plasmonic systems driven by geometric polarization effects, expanding spin-based optical control.

Findings

Observation of spin-momentum locking in symmetric plasmonic structures

Identification of geometric LB-LD effect causing spin-split dispersion

Single-shot polarization-resolved dispersion measurement capability

Abstract

Spin-dependent dispersion and Rashba effect are manifestations of universal spin orbit interaction associated with the breaking of the spatial inversion symmetry in condensed matter and in optical systems. In sharp contrast to this, we report a spin-split dispersion effect of leaky surface plasmons in an inversion-symmetric one dimensional plasmonic grating system. In our system, the signature of spin-momentum locking and the resulting spin-polarization dependent splitting of dispersion of the surface plasmons are observed through the leakage radiation detected in a Fourier (momentum) domain optical arrangement. The setup enables single-shot recording of the full polarization-resolved dispersion (frequency vs transverse momentum (k)) of the leaky surface plasmons. Momentum domain polarization analysis identified a transverse momentum (k) dependent linear birefringence-linear dichroism effect (referred to as the geometric LB-LD effect) responsible for the observed spin-split dispersion. This unconventional SOI effect is reminiscent of the recently reported LB-LD effect resulting in giant chirality in centrosymmetric crystal, albeit with geometric origin. It is demonstrated that the interplay of the geometrical polarization transformation in focused polarized light and subsequent interaction of the structured field polarization with the plasmonic grating leads to the evolution of strong geometrical phase gradient or spin(circular polarization)-dependent transverse momentum of light resulting in spin-split dispersion. Our study offers a new paradigm of spin-based dispersion engineering and spin-enabled nano-optical functionalities in simple symmetric metasurfaces using geometric LB-LD effect.