A tunable topological insulator in the spin helical Dirac transport regime
A tunable topological insulator in the spin helical Dirac transport regime
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自旋螺旋狄拉克输运体系中的可调谐拓扑绝缘体
DOI：
10.1038/nature08234
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发表时间：
2009-08-27
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.;Xia, Y.;Hasan, M. Z.
螺旋狄拉克费米子-电荷载流子，表现为无质量的相对论粒子，其固有角动量（自旋）锁定其平移动量-被认为是实现凝聚态物理学中新现象的关键（1-9）。突出的例子包括磁电耦合的反常量子化（4-6），半费米子态是它们自己的反粒子（7，8），玻色-爱因斯坦凝聚体中的电荷分馏（9），所有这些都是传统的石墨烯种类的狄拉克费米子不可能的（10）。由于缺乏必要的自旋敏感测量，螺旋狄拉克费米子至今仍然难以捉摸，因为这种费米子被禁止存在于含有相对论电子的传统材料中，如石墨烯（10）或铋（11）。最近有人提出，螺旋狄拉克费米子可能存在于某些类型的拓扑有序绝缘体的边缘（3，4，12）-具有自旋轨道起源的体绝缘间隙和表面状态的材料免受时间反演散射的影响-并且如果绝缘体被调谐到所谓的拓扑输运状态，则可以获得它们的特殊性质（3-9）。然而，在现有的拓扑绝缘体中还没有观察到螺旋狄拉克费米子（13-18）。在这里，我们报告的实现和表征的可调拓扑绝缘体铋类材料相结合的自旋成像和动量分辨光谱，体电荷补偿，霍尔传输测量和表面量子控制。我们的研究结果揭示了一个自旋动量锁定狄拉克锥携带一个非平凡的Berry的相位，这是近100%的自旋极化，表现出可调的拓扑费米子密度在附近的Kramers点，可以驱动到长期寻求的拓扑自旋输运制度。所观察到的拓扑节点状态被证明是保护，甚至高达300 K。我们在化学计量比Bi 2Se 3.M-x（M-x表示表面掺杂或门控）中的室温拓扑有序和非平凡自旋织构的演示为未来拓扑绝缘体的石墨烯类研究铺平了道路，以及可能在室温下观察到的自旋极化边缘通道在自旋电子学和计算技术中的应用。
Helical Dirac fermions-charge carriers that behave as massless relativistic particles with an intrinsic angular momentum (spin) locked to its translational momentum-are proposed to be the key to realizing fundamentally new phenomena in condensed matter physics(1-9). Prominent examples include the anomalous quantization of magneto-electric coupling(4-6), half-fermion states that are their own antiparticle(7,8), and charge fractionalization in a Bose-Einstein condensate(9), all of which are not possible with conventional Dirac fermions of the graphene variety(10). Helical Dirac fermions have so far remained elusive owing to the lack of necessary spin-sensitive measurements and because such fermions are forbidden to exist in conventional materials harbouring relativistic electrons, such as graphene(10) or bismuth(11). It has recently been proposed that helical Dirac fermions may exist at the edges of certain types of topologically ordered insulators(3,4,12)-materials with a bulk insulating gap of spin-orbit origin and surface states protected against scattering by time-reversal symmetry-and that their peculiar properties may be accessed provided the insulator is tuned into the so-called topological transport regime(3-9). However, helical Dirac fermions have not been observed in existing topological insulators(13-18). Here we report the realization and characterization of a tunable topological insulator in a bismuth-based class of material by combining spin-imaging and momentum-resolved spectroscopies, bulk charge compensation, Hall transport measurements and surface quantum control. Our results reveal a spin-momentum locked Dirac cone carrying a non-trivial Berry's phase that is nearly 100 per cent spin-polarized, which exhibits a tunable topological fermion density in the vicinity of the Kramers point and can be driven to the long-sought topological spin transport regime. The observed topological nodal state is shown to be protected even up to 300 K. Our demonstration of room-temperature topological order and non-trivial spin-texture in stoichiometric Bi2Se3.M-x (M-x indicates surface doping or gating control) paves the way for future graphene-like studies of topological insulators, and applications of the observed spin-polarized edge channels in spintronic and computing technologies possibly at room temperature.