AI 中文总结
该研究发现极性拓扑绝缘体BiSbTeSe₂因失去反演中心产生巨量体Rashba劈裂，其Rashba系数接近GaAs，可用于研究体Rashba与拓扑表面态的自旋电荷输运贡献。
AI 中文摘要
在Bi₂Se₃或Bi₂Te₃等四碲拓扑绝缘体中，体Rashba自旋劈裂是被禁止的，因为它们的五原子层堆叠结构保持了反演对称性。我们发现BiSbTeSe₂突破了这一限制：在Se-Bi-Se-Sb-Te的序列结构中，该结构失去了反演中心，使Γ点的点群对称性从D₃d降低至C₃v。考虑自旋轨道耦合的第一性原理密度泛函计算表明，这种有序结构仍保留了强拓扑绝缘体的体带反转和线性色散的表面态。此外，其体带在远离Γ点处出现了显著的线性k依赖自旋劈裂。将导带和价带的双重态拟合到受对称性约束的两带k·p哈密顿量，我们提取出本征线性Rashba系数为α_CB≈2.66 eV·Å和α_VB≈0.35 eV·Å。导带的这一数值使有序BiSbTeSe₂跻身于迄今报道的最强体Rashba拓扑绝缘体体系之列，并接近基准极性Rashba半导体GaAs中的耦合强度。因此，有序排列为实现与受保护拓扑表面态共存的巨量体自旋-动量锁定提供了一条途径，为在同一材料中研究体Rashba和拓扑表面对自旋与电荷输运的贡献提供了平台。
英文摘要
Bulk-Rashba spin splitting is forbidden in tetradymite topological insulators like Bi$_2$Se$_3$ or Bi$_2$Te$_3$, since their quintuple-layer stacking preserves inversion symmetry. We show that BiSbTeSe$_2$ escapes this restriction: in the Se-Bi-Se-Sb-Te sequence, the structure loses its inversion center, reducing the point group symmetry at $Γ$ from $D_{3d}$ to $C_{3v}$. First-principles density functional calculations with spin-orbit coupling show that this ordered structure retains bulk band inversion and a linearly dispersive surface state of a strong topological insulator. Additionally, its bulk bands acquire a pronounced linear-in-$k$ spin splitting away from $Γ$. Fitting the conduction- and valence-band doublets to symmetry-constrained two-band $k\cdot p$ Hamiltonians, we extract intrinsic linear Rashba coefficients of $α_{\mathrm{CB}}\approx2.66~\mathrm{eV\,\textÅ}$ and $α_{\mathrm{VB}}\approx0.35~\mathrm{eV\,\textÅ}$. The conduction-band value places ordered BiSbTeSe$_2$ among the strongest bulk-Rashba topological-insulator systems reported to date and approaches the coupling found in the benchmark polar Rashba semiconductor BiTeI. Sublattice ordering thus provides a route to giant bulk spin--momentum locking that coexists with protected topological surface states, offering a platform in which bulk-Rashba and topological surface contributions to spin and charge transport can be investigated within the same material.
Comments14 pages, 11 figures
