Spin–orbit coupling forms the physical basis for quantum materials with non-trivial topology and potential spintronics applications. The Rashba interaction is a textbook model of spin–orbit interactions, with charge carriers undergoing linear, isotropic spin-splitting in momentum space. Recently, non-centrosymmetric semiconductors in the family BiTeX (X = Cl, Br, I) have been identified as exemplary Rashba materials due to the strong splitting of their bulk bands, yet a detailed investigation of their spin textures, and their relationships to local crystal symmetry, is currently lacking. We perform high-efficiency spin-resolved photoemission spectroscopy to directly image the spin texture of surface states of BiTeCl, and we find dramatic deviations from idealized behavior, including a reversal of the spin-polarization near the Fermi level. We show that this behavior can be described by higher-order contributions to the canonical Rashba model with the surface states localized to individual trilayers of the crystal. Due to the prominence of these effects near the Fermi level, they should have a strong impact on the spin-dependent transport of carriers.

自旋轨道耦合构成了具有非平凡拓扑结构和潜在自旋电子学应用的量子材料的物理基础。Rashba 相互作用是自旋轨道相互作用的教科书模型，电荷载流子在动量空间中经历线性、各向同性的自旋分裂。最近，BiTe X家族中的非中心对称半导体（X = Cl, Br, I) 由于其体能带的强烈分裂而被确定为典型的 Rashba 材料，但目前缺乏对其自旋纹理及其与局部晶体对称性的关系的详细研究。我们执行高效自旋分辨光电子能谱以直接成像 BiTeCl 表面状态的自旋纹理，我们发现与理想化行为的显着偏差，包括费米能级附近的自旋极化反转。我们表明，这种行为可以通过对典型 Rashba 模型的高阶贡献来描述，其中表面状态局限于晶体的各个三层。由于这些效应在费米能级附近很突出，它们应该对载流子的自旋相关输运产生强烈影响。