Department of Materials Science and Engineering, Zhejiang University , Hangzhou 310027, China.
Nano Lett. 2015 Jan 14;15(1):80-7. doi: 10.1021/nl502997v. Epub 2014 Dec 12.
Topological insulators (TIs) are a new type of electronic materials in which the nontrivial insulating bulk band topology governs conducting boundary states with embedded spin-momentum locking. Such edge states are more robust in a two-dimensional (2D) TI against scattering by nonmagnetic impurities than in its three-dimensional (3D) variant, because in 2D the two helical edge states are protected from the only possible backscattering. This makes the 2D TI family a better candidate for coherent spin transport and related applications. While several 3D TIs are already synthesized experimentally, physical realization of 2D TI is so far limited to hybrid quantum wells with a tiny bandgap that does not survive temperatures above 10 K. Here, combining first-principles calculations and scanning tunneling microscopy/spectroscopy (STM/STS) experimental studies, we report nontrivial 2D TI phases in 2-monolayer (2-ML) and 4-ML Bi(110) films with large and tunable bandgaps determined by atomic buckling of Bi(110) films. The gapless edge states are experimentally detected within the insulating bulk gap at 77 K. The band topology of ultrathin Bi(110) films is sensitive to atomic buckling. Such buckling is sensitive to charge doping and could be controlled by choosing different substrates on which Bi(110) films are grown.
拓扑绝缘体(TIs)是一种新型的电子材料,其非平凡的绝缘体带拓扑结构控制着具有内置自旋动量锁定的导电边界态。与三维(3D)变体相比,二维(2D)TI 中的这些边缘态在受到非磁性杂质散射时更加稳定,因为在 2D 中,两个螺旋边缘态不受唯一可能的反向散射的影响。这使得 2D TI 家族成为相干自旋输运和相关应用的更好候选者。虽然已经有几种 3D TI 在实验中被合成,但 2D TI 的物理实现迄今为止仅限于具有微小带隙的混合量子阱,该带隙在 10 K 以上的温度下无法存活。在这里,我们结合第一性原理计算和扫描隧道显微镜/光谱(STM/STS)实验研究,报告了在具有大可调带隙的 2 单层(2-ML)和 4 单层 Bi(110)薄膜中存在非平凡的 2D TI 相,该带隙由 Bi(110)薄膜的原子弯曲决定。在 77 K 下,在绝缘体带隙内实验检测到无带隙边缘态。超薄 Bi(110)薄膜的能带拓扑结构对原子弯曲敏感。这种弯曲对电荷掺杂敏感,可以通过选择在其上生长 Bi(110)薄膜的不同衬底来控制。