Hsieh D, Xia Y, Qian D, Wray L, Dil J H, Meier F, Osterwalder J, Patthey L, Checkelsky J G, Ong N P, Fedorov A V, Lin H, Bansil A, Grauer D, Hor Y S, Cava R J, Hasan M Z
Joseph Henry Laboratories of Physics, Department of Physics, Princeton University, Princeton, New Jersey 08544, USA.
Nature. 2009 Aug 27;460(7259):1101-5. doi: 10.1038/nature08234. Epub 2009 Jul 20.
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. Prominent examples include the anomalous quantization of magneto-electric coupling, half-fermion states that are their own antiparticle, and charge fractionalization in a Bose-Einstein condensate, all of which are not possible with conventional Dirac fermions of the graphene variety. 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 or bismuth. It has recently been proposed that helical Dirac fermions may exist at the edges of certain types of topologically ordered insulators-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. However, helical Dirac fermions have not been observed in existing topological insulators. 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 Bi(2)Se(3).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.
螺旋狄拉克费米子——一种电荷载流子，其行为如同无质量的相对论粒子，具有与平移动量锁定的内禀角动量（自旋）——被认为是在凝聚态物理中实现全新现象的关键。突出的例子包括磁电耦合的反常量子化、自身为反粒子的半费米子态以及玻色 - 爱因斯坦凝聚体中的电荷分数化，所有这些对于石墨烯类的传统狄拉克费米子而言都是不可能的。由于缺乏必要的自旋敏感测量，并且因为这种费米子被禁止存在于诸如石墨烯或铋等含有相对论电子的传统材料中，螺旋狄拉克费米子至今仍难以捉摸。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——这类材料具有自旋轨道起源的体能隙以及由时间反演对称性保护免受散射的表面态——并且只要将绝缘体调谐到所谓的拓扑输运 regime，就可以探究它们的奇特性质。然而，在现有的拓扑绝缘体中尚未观察到螺旋狄拉克费米子。在此，我们通过结合自旋成像和动量分辨光谱、体电荷补偿、霍尔输运测量以及表面量子控制，报告了在铋基材料类中实现并表征了一种可调谐拓扑绝缘体。我们的结果揭示了一个自旋 - 动量锁定的狄拉克锥，其携带一个几乎 100%自旋极化的非平凡贝里相位，在克莱默斯点附近表现出可调谐的拓扑费米子密度，并且可以被驱动到长期寻求的拓扑自旋输运 regime。所观察到的拓扑节点态即使在高达 300 K 时仍被证明是受保护的。我们在化学计量比的 Bi(2)Se(3).M(x)（M(x)表示表面掺杂或栅极控制）中实现室温拓扑序和非平凡自旋纹理的演示，为未来对拓扑绝缘体进行类似石墨烯的研究以及在可能的室温自旋电子学和计算技术中应用所观察到的自旋极化边缘通道铺平了道路。
