Large-area robust pure one-way bulk states in a square photonic reduced Haldane model

The coexistence of antichiral one-way edge states (AOWESs) and one-way bulk states (OWBSs) has recently been investigated in honeycomb photonic crystals, yet their realization in square photonic crystals, which is crucial for achieving a complete understanding and broader applicability of such topological phenomena, has not been reported. In this work, we propose a two-dimensional (2D) square photonic reduced Haldane model by applying opposing magnetic fields to yttrium iron garnet cylinders in adjacent rows to effectively analogize the horizontal hoppings in electronic systems. This model simultaneously supports both AOWESs and OWBSs. Remarkably, in both the theoretical analysis and experimental realizations of 2D air-loaded square gyromagnetic photonic crystals based on this model, we demonstrate that counter-propagating AOWESs above the light cone can be suppressed through appropriate scattering boundary conditions, resulting in a system that exclusively hosts pure OWBSs. These bulk states are further shown to enable robust, large-area one-way transport of electromagnetic waves. Our findings not only expand the understanding of topological states in square fermionic and bosonic systems, but also open new avenues for the development of robust, large-area energy transmission devices featuring unidirectional conduction.