Giant photonic spin Hall effect in momentum space in a structured metamaterial with spatially varying birefringence

The photonic spin Hall effect (SHE) in the reflection and refraction at an interface is very weak because of the weak spin-orbit interaction. Here, we report the observation of a giant photonic SHE in a dielectric-based metamaterial. The metamaterial is structured to create a coordinate-dependent, geometric Pancharatnam–Berry phase that results in an SHE with a spin-dependent splitting in momentum space. It is unlike the SHE that occurs in real space in the reflection and refraction at an interface, which results from the momentum-dependent gradient of the geometric Rytov–Vladimirskii–Berry phase. We theorize a unified description of the photonic SHE based on the two types of geometric phase gradient, and we experimentally measure the giant spin-dependent shift of the beam centroid produced by the metamaterial at a visible wavelength. Our results suggest that the structured metamaterial offers a potential method of manipulating spin-polarized photons and the orbital angular momentum of light and thus enables applications in spin-controlled nanophotonics. A giant photonic spin Hall effect (SHE) has been predicted and experimentally observed in a dielectric metamaterial by scientists in China. The conventional SHE that occurs when light is reflected or refracted at an interface is inherently weak due to the weak spin–orbit interaction. Now, researchers at Hunan University, Hengyang Normal University and Shenzhen University have theoretically predicted and experimentally confirmed a giant SHE in a metamaterial structured to produce the Pancharatnam–Berry phase in one dimension and having a spatially varying birefringence. Unlike the tiny real-space shift induced by the Rytov–Vladimirskii–Berry phase gradient, the giant SHE occurs in momentum space and is sufficiently large to be observed directly. Such metamaterials could potentially be used to manipulate spin-polarized photons and the orbital angular momentum of light, enabling applications in spin-controlled nanophotonics.