Spin-orbit-locked hyperbolic polariton vortices carrying reconfigurable topological charges

Abstract

The topological features of optical vortices have been opening opportunities for free-space and on-chip photonic technologies, e.g., for multiplexed optical communications and robust information transport. In a parallel but disjoint effort, polar anisotropic van der Waals nanomaterials supporting hyperbolic phonon polaritons (HP ²s) have been leveraged to drastically boost light-matter interactions. So far HP ² studies have been mainly focusing on the control of their amplitude and scale features. Here we report the generation and observation of mid-infrared hyperbolic polariton vortices (HP ²Vs) associated with reconfigurable topological charges. Spiral-shaped gold disks coated with a flake of hexagonal boron nitride are exploited to tailor spin–orbit interactions and realise deeply subwavelength HP ²Vs. The complex interplay between excitation spin, spiral geometry and HP ² dispersion enables robust reconfigurability of the associated topological charges. Our results reveal unique opportunities to extend the application of HP ²s into topological photonics, quantum information processing by integrating these phenomena with single-photon emitters, robust on-chip optical applications, sensing and nanoparticle manipulation.