Prediction and Observation of Robust One-Way Bulk States in a Gyromagnetic Photonic Crystal.

We report a two-dimensional heterogeneous Haldane model composed of alternately stacking modified Haldane lattices with opposite next-nearest-neighbor hoppings, and predict the emergence of robust one-way bulk states by an ab initio theoretical calculation. These unique bulk states transport unidirectionally and are robust against backscattering from impurities in the strip bulk. By analogy with the heterogeneous Haldane model, we further confirm by numerical simulations and experimental measurements the existence of robust one-way bulk states in a two-dimensional microwave gyromagnetic photonic crystal, and demonstrate their robust one-way property over a long-distance even in the presence of metallic obstacles. Our study provides the strong support for the generalization and application of band theories to fermionic and bosonic systems, and paves a way for the implementation of high-throughput robust energy transmission materials and devices.