拓扑绝缘体和拓扑晶体绝缘体的制备和性质研究
发布时间：2019-06-22 12:27
【摘要】：拓扑绝缘体和拓扑晶体绝缘体是一类新奇量子物态。它们的共同特点是:在绝缘的体电子态之间存在无能隙的自旋极化的表面态,这种表面态跟表面结构无关,由体态的拓扑性质决定。这些新奇的物理性质使它们在自旋电子学和拓扑量子计算等领域具有非常大的应用潜力。而制备出高质量的拓扑绝缘体和拓扑晶体绝缘体材料是制备电子器件以及研究这种量子态本质的关键。在本论文的实验工作中,我们结合超高真空的分子束外延(MBE)、扫描隧道显微镜(STM)和角分辨光电子能谱(ARPES)等手段研究了高质量的拓扑晶体绝缘体(NaCl-type的SnSe)的生长动力学以及电子结构,并对拓扑绝缘体的拓扑相变和热电性质做了详细的研究。论文的主要成果总结如下:(1)我们利用MBE在Bi_2Se_3薄膜上外延出了高质量的NaCl-type的SnSe薄膜,确定了NaCl-type的SnSe薄膜的生长动力学条件。结合第一性原理计算和ARPES结果,我们首次确定了NaCl-type的SnSe是一种新的拓扑晶体绝缘体。(2)采用MBE的生长方式,我们在单层的Graphene上生长出了高质量的(Bi1-xInx)2Se3(0≤x≤1)薄膜。并对这种体系进行了详细的变层厚的ARPES研究,给出了这个体系的相变点:拓扑相变点在5%到9%之间,当掺In量5%时,(Bi1-xInx)2Se3体系属于拓扑非平庸态;当掺In量9%时,(Bi1-xInx)2Se3体系属于拓扑平庸态。通过对ARPES结果的分析,我们首次证实:当In掺杂到Bi_2Se_3体系中时,体系的体态能隙减小,体态能隙的减小会造成表面态的穿透深度增加,当体态能隙减小到一定程度,表面态的穿透深度足够深时,上下表面态就可以发生耦合,Dirac型表面态在发生拓扑相变之前打开能隙。另外,我们在α-In2Se3(厚度小于4QL)和Graphene的范德瓦尔斯异质结中发现了很强的能带调控效应,我们推测这种调控的能带属于超晶格Dirac点。为了证明这种猜测,我们正在做理论模拟。(3)我们采用MBE在高阻STO(111)面上生长出了高质量的Bi_2Se_3薄膜,并对Bi_2Se_3薄膜进行了变层厚的热电输运的测量。我们发现Bi_2Se_3薄膜的热电势的绝对值以及功率因子随层厚的增加而增加。我们希望跟理论模拟结合给出一种能够继续提高像Bi_2Se_3、Sb2Te3等拓扑绝缘体材料的热电性质的方法。
[Abstract]:Topological insulators and topological crystal insulators are a kind of novel quantum states. Their common characteristics are that there is a spin-polarized surface state without energy gap between the electronic states of the insulated body, which is independent of the surface structure and determined by the topological properties of the body state. These novel physical properties make them have great application potential in the fields of spin electronics and topological quantum computing. The preparation of high quality topological insulators and topological crystal insulators is the key to the fabrication of electronic devices and the study of the nature of this quantum state. In this thesis, the growth kinetics and electronic structure of high quality topological crystal insulators (SnSe) were studied by using ultra-high vacuum molecular beam epitaxial (MBE), scanning tunneling microscope (STM) and angle-resolved photoelectron spectroscopy (ARPES). The topological phase transition and thermoelectric properties of topological insulators were studied in detail. The main results of this paper are summarized as follows: (1) High quality NaCl-type SnSe thin films were epitaxial on Bi_2Se_3 thin films by MBE, and the growth kinetics conditions of NaCl-type SnSe thin films were determined. Combined with the first principle calculation and ARPES results, we determine for the first time that the SnSe of NaCl-type is a new topological crystal insulator. (2) by using the growth mode of MBE, we have grown high quality (Bi1-xInx) 2Se3 (0 鈮，
本文编号：2504581
[Abstract]:Topological insulators and topological crystal insulators are a kind of novel quantum states. Their common characteristics are that there is a spin-polarized surface state without energy gap between the electronic states of the insulated body, which is independent of the surface structure and determined by the topological properties of the body state. These novel physical properties make them have great application potential in the fields of spin electronics and topological quantum computing. The preparation of high quality topological insulators and topological crystal insulators is the key to the fabrication of electronic devices and the study of the nature of this quantum state. In this thesis, the growth kinetics and electronic structure of high quality topological crystal insulators (SnSe) were studied by using ultra-high vacuum molecular beam epitaxial (MBE), scanning tunneling microscope (STM) and angle-resolved photoelectron spectroscopy (ARPES). The topological phase transition and thermoelectric properties of topological insulators were studied in detail. The main results of this paper are summarized as follows: (1) High quality NaCl-type SnSe thin films were epitaxial on Bi_2Se_3 thin films by MBE, and the growth kinetics conditions of NaCl-type SnSe thin films were determined. Combined with the first principle calculation and ARPES results, we determine for the first time that the SnSe of NaCl-type is a new topological crystal insulator. (2) by using the growth mode of MBE, we have grown high quality (Bi1-xInx) 2Se3 (0 鈮，
本文编号：2504581
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