Robust Spin‐Momentum Coupling Induced by Parity‐Time Symmetric Spatiotemporal Metasurface

Abstract Topological effects have endowed brand new properties to electronic and photonic systems, including the unidirectional propagating edge states and the associated intrinsic robustness. Recent progress in topological photonics has explored novel optical effects and motivated the related photonic devices. Here, a new mechanism for controlling the electromagnetic wave flow based on spatiotemporal metasurface assisted with parity‐time (PT) symmetric modulations is proposed, and a proof‐in‐principle experiment is conducted in the microwave regime for verification. It is shown that the spatiotemporal metasurface can provide a powerful platform for realizing robust spin‐momentum coupled surface states, in which the induced effects are similar to those discovered in the topological insulators and quantum spin‐Hall systems. With the aid of programmable control unit, the generated spin‐momentum coupling can be flexibly switched in real time. The proposed scheme is expected to construct a novel system for controlling the evanescent light flows and facilitate the investigation of physical effects that are hard to realize in the traditional photonic topological systems.