Topological surface states protected from backscattering by chiral spin texture
Topological surface states protected from backscattering by chiral spin texture
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DOI：
10.1038/nature08308
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发表时间：
2009-08-27
期刊：
影响因子：
64.8
通讯作者：
Yazdani, Ali
中科院分区：
文献类型：
--
作者：
Roushan, Pedram;Seo, Jungpil;Yazdani, Ali
拓扑绝缘体是一类新型绝缘体，由于这些系统固有的强自旋轨道耦合(1-5)，其中会产生电子激发的体间隙。这些材料与普通绝缘体的区别在于存在无间隙金属表面态，类似于量子霍尔系统中的手性边缘模式，但具有非常规的自旋纹理。这种自旋纹理边界态的一个关键预测特征是它们对自旋无关散射不敏感，这被认为可以保护它们免受反向散射和局域化。最近，实验和理论工作为半导体量子阱结构（6-8）和几种铋基化合物（9-13）中此类拓扑绝缘体材料的二维和三维类别的存在提供了强有力的证据，但迄今为止实验尚未探讨这些手性态对散射的敏感性。在这里，我们使用扫描隧道光谱和角分辨光电子能谱来可视化三维拓扑绝缘体 Bi1-xSbx 中的无间隙表面态，并详细检查该化合物中随机合金化引起的无序散射的影响。我们表明，尽管原子尺度无序性很强，但相反动量和相反自旋状态之间的反向散射并不存在。我们的观察表明，这些状态的手性性质保护了载流子的自旋。因此，这些手性态对于基于自旋的电子学（其中长自旋相干性至关重要（14））以及量子计算应用（其中拓扑保护可以实现容错信息处理）可能有用（15,16）。
Topological insulators are a new class of insulators in which a bulk gap for electronic excitations is generated because of the strong spin-orbit coupling(1-5) inherent to these systems. These materials are distinguished from ordinary insulators by the presence of gapless metallic surface states, resembling chiral edge modes in quantum Hall systems, but with unconventional spin textures. A key predicted feature of such spin-textured boundary states is their insensitivity to spin-independent scattering, which is thought to protect them from backscattering and localization. Recently, experimental and theoretical efforts have provided strong evidence for the existence of both two-and three-dimensional classes of such topological insulator materials in semiconductor quantum well structures(6-8) and several bismuth-based compounds(9-13), but so far experiments have not probed the sensitivity of these chiral states to scattering. Here we use scanning tunnelling spectroscopy and angle-resolved photoemission spectroscopy to visualize the gapless surface states in the three-dimensional topological insulator Bi1-xSbx, and examine in detail the influence of scattering from disorder caused by random alloying in this compound. We show that, despite strong atomic scale disorder, backscattering between states of opposite momentum and opposite spin is absent. Our observations demonstrate that the chiral nature of these states protects the spin of the carriers. These chiral states are therefore potentially useful for spin-based electronics, in which long spin coherence is critical(14), and also for quantum computing applications, where topological protection can enable fault-tolerant information processing(15,16).