A topological Dirac insulator in a quantum spin Hall phase
A topological Dirac insulator in a quantum spin Hall phase
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DOI：
10.1038/nature06843
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发表时间：
2008-04-24
期刊：
影响因子：
64.8
通讯作者：
Hasan, M. Z.
中科院分区：
文献类型：
--
作者：
Hsieh, D.;Qian, D.;Hasan, M. Z.
当电子受到一个大的外部磁场，传统的电荷量子霍尔效应（1，2）规定，电子激发间隙中产生的样品块，但金属导电允许在边界。最近的理论模型表明，某些具有大的自旋-轨道相互作用的大块绝缘体也可能自然地支持量子极限中的导电拓扑边界态（3-5），这为研究零外部磁场中不寻常的量子霍尔现象开辟了可能性（6）。据预测，大块Bi 1-xSbx单晶是一种被称为拓扑绝缘体（9-11）的不寻常霍尔相物质的主要候选者（7，8）。拓扑绝缘体的标志是存在金属表面态，其是表征量子自旋霍尔绝缘体的边缘态的高维类似物（3-13）。除了其令人感兴趣的边界状态之外，预测Bi 1-xSbx的本体表现出三维狄拉克粒子（14-17），这是继在二维石墨烯（18-20）中的新发现和在纯铋（21）中观察到的电荷量子霍尔分馏之后的另一个当前高度感兴趣的主题。然而，尽管自20世纪60年代以来对Bi 1-xSbx家族进行了大量的输运和磁性测量（17），但没有发现拓扑霍尔态或体狄拉克粒子的直接证据。（IPEM-ARPES），我们报告了在Bi 0.9Sb 0.1体块中直接观察到的大量狄拉克粒子，在样品的边界处定位Kramers点，并提供狄拉克绝缘体的无隙表面电子带的全面映射。这些发现表明，在大块绝缘体的边界上观察到的表面态是“拓扑金属”的实现（9-11）。他们还建议，这种材料在开发下一代量子计算设备方面具有潜在的应用，这些设备可能会结合“类光”的散装载体和自旋纹理表面电流。
When electrons are subject to a large external magnetic field, the conventional charge quantum Hall effect(1,2) dictates that an electronic excitation gap is generated in the sample bulk, but metallic conduction is permitted at the boundary. Recent theoretical models suggest that certain bulk insulators with large spin - orbit interactions may also naturally support conducting topological boundary states in the quantum limit(3-5), which opens up the possibility for studying unusual quantum Hall- like phenomena in zero external magnetic fields(6). Bulk Bi1-xSbx single crystals are predicted to be prime candidates(7,8) for one such unusual Hall phase of matter known as the topological insulator(9-11). The hallmark of a topological insulator is the existence of metallic surface states that are higher- dimensional analogues of the edge states that characterize a quantum spin Hall insulator(3-13). In addition to its interesting boundary states, the bulk of Bi1-xSbx is predicted to exhibit three- dimensional Dirac particles(14-17), another topic of heightened current interest following the new findings in two-dimensional graphene(18-20) and charge quantum Hall fractionalization observed in pure bismuth(21). However, despite numerous transport and magnetic measurements on the Bi1-xSbx family since the 1960s(17), no direct evidence of either topological Hall states or bulk Dirac particles has been found. Here, using incident- photon- energy- modulated angle- resolved photoemission spectroscopy ( IPEM- ARPES), we report the direct observation of massive Dirac particles in the bulk of Bi0.9Sb0.1, locate the Kramers points at the sample's boundary and provide a comprehensive mapping of the Dirac insulator's gapless surface electron bands. These findings taken together suggest that the observed surface state on the boundary of the bulk insulator is a realization of the 'topological metal'(9-11). They also suggest that this material has potential application in developing next- generation quantum computing devices that may incorporate 'light- like' bulk carriers and spin- textured surface currents.