Emergent Spin-Momentum Locking Phenomena in Low-Dimensional Perovskites.

Chiral hybrid organic-inorganic pyramidal perovskites provide a fertile platform for spin-orbit-driven functionalities. Using first-principles calculations, we show that chiral cation substitution in quasi-one-dimensional Pb-Br pyramidal chains induces sizable spin splitting (up to ∼170 meV) and an emergent one-dimensional (1D) spin-momentum locking near the band edges. Although the nonsymmorphic chiral space group permits independent linear spin-orbit coupling channels along all three spatial directions, the electronic structure self-selects a single dominant channel due to a symmetry-dimensionality mismatch between the three-dimensional (3D) chiral lattice and the quasi-one-dimensional electronic manifold. This mechanism is not symmetry-enforced but emergent, and establishes a transferable physical principle for engineering spin textures in low-dimensional chiral solids.