论文标题：Observation of a topological insulator Dirac cone reshaped by non-magnetic impurity resonance

期刊：npj Quantum Materials

作者：Lin Miao, Yishuai Xu, Wenhan Zhang, Daniel Older, S. Alexander Breitweiser, Erica Kotta, Haowei He, Takehito Suzuki, Jonathan D. Denlinger, Rudro R. Biswas, Joseph G. Checkelsky, Weida Wu & L. Andrew Wray

发表时间：2018/06/04

数字识别码：10.1038/s41535-018-0101-8

原文链接： https://www.nature.com/articles/s41535-018-0101-8?utm_source=Other_website&utm_medium=Website_links&utm_content=JesGuo-Nature-npj_Quantum_Materials-Materials_Science-China&utm_campaign=NPJ_USG_JRCN_JG_npj_Aug_Dirac_sciencenet

受背散射和安德森局域化内在的免疫性，拓扑绝缘体电子性质很少受干扰，尤其非磁性杂质的影响。但最近理论研究表明，表面杂质在接近狄拉克点附近产生共振态。当杂质态密度达到实验上可观测水平时，杂质共振态将表现为平能带与上狄拉克锥紧密杂化，从而将狄拉克带分裂为上下两个分支。最新扫描隧道显微镜(STM)实验也为这种新奇准粒子行为提供了定量证据。但是相对更大尺度的直观形态表征，例如角分辨光电子能谱(ARPES)，以及非磁性无序如何重塑拓扑狄拉克锥，尚未有报道。

近日，来自美国普渡大学Andrew Wray教授领衔国际团队，利用高分辨线性-二色性ARPES，在富含缺陷的拓扑绝缘体Bi2Se3中观测到了狄拉克锥的重塑。如图1所示，狄拉克点以上40 meV存在反常扭结状的扩散行为，与理论模拟相吻合(图2)。随着低温热处理时间增加，缺陷杂质密度减少，ARPES数据表现出显著的清晰带。

图1： ARPES测量缺陷诱导的能谱扩散异常。狄拉克锥带结构的对称π和σ-pol ARPES图像(a) 低温热处理前；(b) 热处理1 h；(c) 热处理3 h。对应模拟与不同处理时间的(d-g)动量分布曲线与(h-k) 拟合曲线。

图2：理论模拟Bi2Se3在动量空间的杂质共振。(a) 模拟无杂质下的狄拉克锥；(b) 标量杂质密度ρ=0.06%下狄拉克锥的重塑；(c) Dirac锥通过参与比率加权以突出杂质共振状态；(d) 相应DOS曲线。

需要注意的是，杂质共振的基本特性是存在共振能量下的DOS峰值。而Luttinger理论不适用于无序系统，因此ARPES的能带色散关系无法分辨DOS峰。他们在二维动量空间上对ARPES谱函数求和，利用狄拉克点附近的连续旋转对称来定义DOS(E)。将该对称化程序分别应用于σ-pol和π-pol二向色性ARPES数据，获得了表面态DOS的不同加权近似(图3)，与模拟结果相吻合。以上研究进展为重塑拓扑绝缘体表面态的物理机制提供实验依据。

图3：杂质共振DOS峰。(a) σ-pol和π-pol二向色性ARPES数据中得到的不同杂质密度下的DOS曲线；(b) 理论模拟结果。

摘要：The massless Dirac electrons found at topological insulator surfaces are thought to be influenced very little by weak, non-magnetic disorder. However, a resonance effect of strongly perturbing non-magnetic impurities has been theoretically predicted to change the dispersion and physical nature of low-energy quasiparticles, resulting in unique particle-like states that lack microscopic translational symmetry. Here we report the direct observation of impurities reshaping the surface Dirac cone of the model three-dimensional topological insulator bismuth selenide. A pronounced kink-like dispersion feature is observed in disorder-enriched samples, and found to be closely associated with the anomaly caused by impurity resonance in the surface state density of states, as observed by dichroic angle-resolved photoemission spectroscopy. The experimental observation of these features, which closely resemble theoretical predictions, has significant implications for the properties of topological Dirac cones in applied scenarios that commonly feature point-defect disorder at surfaces or interfaces.

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期刊介绍：

npj Quantum Materials is an online-only, open access journal, publishing original research results and reviews on broad coverage of quantum materials, their fundamental properties, fabrication and applications.

来源：科学网