Half-Chern-Layer Axion Insulator with Reconfigurable Spin–Chirality Hinges

Abstract

Coupled Chern layers can realize axion insulators, but topological gap retention and spin-selective hinge control remain material challenges. We propose a material-design strategy using inversion-symmetric half-Chern layers, exemplified by an antiferromagnetic Ni2I2 stack. Opposite odd-Chern layers at inequivalent inversion embeddings fix an axionic decoupled reference. Interlayer-centered parity–time symmetry and half-Chern spin selectivity help retain the layer-derived gap upon coupling. First-principles calculations predict an axion insulator with a 163 meV bulk gap. A material-informed model shows how interlayer coupling gaps the Chern-layer edge-state manifold, leaving termination-dependent chiral hinge channels. Reversing transverse canting relocates a hinge channel and reverses its propagation while retaining the dominant longitudinal-spin sign inherited from its terminal layer. Layer parity selects relative hinge arrangements and spin sectors, enabling coordinated control of position, chirality, and longitudinal spin.