Chong Su Kong, Han Kyu Bum, Nagaoka Akira, Tsuchikawa Ryuichi, Liu Renlong, Liu Haoliang, Vardeny Zeev Valy, Pesin Dmytro A, Lee Changgu, Sparks Taylor D, Deshpande Vikram V
Department of Physics and Astronomy , University of Utah , Salt Lake City , Utah 84112 , United States.
Department of Materials Science and Engineering , University of Utah , Salt Lake City , Utah 84112 , United States.
Nano Lett. 2018 Dec 12;18(12):8047-8053. doi: 10.1021/acs.nanolett.8b04291. Epub 2018 Nov 9.
Three dimensional (3D) topological insulators (TIs) are an important class of materials with applications in electronics, spintronics and quantum computing. With the recent development of truly bulk insulating 3D TIs, it has become possible to realize surface dominated phenomena in electrical transport measurements e.g. the quantum Hall (QH) effect of massless Dirac fermions in topological surface states (TSS). However, to realize more advanced devices and phenomena, there is a need for a platform to tune the TSS or modify them e.g. gap them by proximity with magnetic insulators, in a clean manner. Here we introduce van der Waals (vdW) heterostructures in the form of topological insulator/insulator/graphite to effectively control chemical potential of the TSS. Two types of gate dielectrics, normal insulator hexagonal boron nitride (hBN) and ferromagnetic insulator CrGeTe (CGT) are utilized to tune charge density of TSS in the quaternary TI BiSbTeSe. hBN/graphite gating in the QH regime shows improved quantization of TSS by suppression of magnetoconductivity of massless Dirac fermions. CGT/graphite gating of massive Dirac fermions in the QH regime yields half-quantized Hall conductance steps and a measure of the Dirac gap. Our work shows the promise of the vdW platform in creating advanced high-quality TI-based devices.
三维（3D）拓扑绝缘体（TIs）是一类重要的材料，在电子学、自旋电子学和量子计算领域有应用。随着真正的体绝缘3D TIs的最新发展，在电输运测量中实现表面主导现象成为可能，例如拓扑表面态（TSS）中无质量狄拉克费米子的量子霍尔（QH）效应。然而，为了实现更先进的器件和现象，需要一个平台来以一种干净的方式调节TSS或对其进行修改，例如通过与磁性绝缘体接近使其带隙。在这里，我们引入拓扑绝缘体/绝缘体/石墨形式的范德华（vdW）异质结构，以有效控制TSS的化学势。利用两种类型的栅极电介质，即普通绝缘体六方氮化硼（hBN）和铁磁绝缘体CrGeTe（CGT），来调节四元TI BiSbTeSe中TSS的电荷密度。在QH regime中，hBN/石墨栅控通过抑制无质量狄拉克费米子的磁导率显示出TSS的量子化得到改善。在QH regime中，对有质量狄拉克费米子进行CGT/石墨栅控产生半量子化的霍尔电导台阶和狄拉克带隙的度量。我们的工作展示了vdW平台在创建先进的高质量基于TI的器件方面的前景。
