Nakamura Hisao, Hofmann Johannes, Inoue Nobuki, Koelling Sebastian, Koenraad Paul M, Mussler Gregor, Grützmacher Detlev, Narayan Vijay
CD-FMat, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba Central 2, Tsukuba, Japan.
Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge, CB3 0FS, UK.
Sci Rep. 2020 Dec 11;10(1):21806. doi: 10.1038/s41598-020-76885-7.
The interface between topological and normal insulators hosts metallic states that appear due to the change in band topology. While topological states at a surface, i.e., a topological insulator-air/vacuum interface, have been studied intensely, topological states at a solid-solid interface have been less explored. Here we combine experiment and theory to study such embedded topological states (ETSs) in heterostructures of GeTe (normal insulator) and [Formula: see text] [Formula: see text] (topological insulator). We analyse their dependence on the interface and their confinement characteristics. First, to characterise the heterostructures, we evaluate the GeTe-Sb[Formula: see text]Te[Formula: see text] band offset using X-ray photoemission spectroscopy, and chart the elemental composition using atom probe tomography. We then use first-principles to independently calculate the band offset and also parametrise the band structure within a four-band continuum model. Our analysis reveals, strikingly, that under realistic conditions, the interfacial topological modes are delocalised over many lattice spacings. In addition, the first-principles calculations indicate that the ETSs are relatively robust to disorder and this may have practical ramifications. Our study provides insights into how to manipulate topological modes in heterostructures and also provides a basis for recent experimental findings [Nguyen et al. Sci. Rep. 6, 27716 (2016)] where ETSs were seen to couple over thick layers.
拓扑绝缘体与普通绝缘体的界面处存在由于能带拓扑变化而出现的金属态。虽然表面的拓扑态，即拓扑绝缘体 - 空气/真空界面处的拓扑态已得到深入研究，但固 - 固界面处的拓扑态研究较少。在此，我们结合实验与理论来研究碲化锗（普通绝缘体）和五碲化锑（拓扑绝缘体）异质结构中的这种嵌入式拓扑态（ETSs）。我们分析它们对界面的依赖性及其受限特性。首先，为了表征异质结构，我们使用X射线光电子能谱评估碲化锗 - 五碲化锑的带隙偏移，并使用原子探针断层扫描绘制元素组成。然后，我们使用第一性原理独立计算带隙偏移，并在四能带连续模型中对能带结构进行参数化。我们的分析惊人地揭示，在实际条件下，界面拓扑模式在许多晶格间距上是离域的。此外，第一性原理计算表明，ETSs对无序相对稳健，这可能具有实际影响。我们的研究为如何在异质结构中操纵拓扑模式提供了见解，也为最近的实验发现[Nguyen等人，《科学报告》6，27716（2016）]提供了基础，在该实验中观察到ETSs在厚层上耦合。
