【摘要】：拓撲絕緣體和拓撲晶體絕緣體是一類新奇量子物態(tài)。它們的共同特點是:在絕緣的體電子態(tài)之間存在無能隙的自旋極化的表面態(tài),這種表面態(tài)跟表面結(jié)構(gòu)無關(guān),由體態(tài)的拓撲性質(zhì)決定。這些新奇的物理性質(zhì)使它們在自旋電子學(xué)和拓撲量子計算等領(lǐng)域具有非常大的應(yīng)用潛力。而制備出高質(zhì)量的拓撲絕緣體和拓撲晶體絕緣體材料是制備電子器件以及研究這種量子態(tài)本質(zhì)的關(guān)鍵。在本論文的實驗工作中,我們結(jié)合超高真空的分子束外延(MBE)、掃描隧道顯微鏡(STM)和角分辨光電子能譜(ARPES)等手段研究了高質(zhì)量的拓撲晶體絕緣體(NaCl-type的SnSe)的生長動力學(xué)以及電子結(jié)構(gòu),并對拓撲絕緣體的拓撲相變和熱電性質(zhì)做了詳細的研究。論文的主要成果總結(jié)如下:(1)我們利用MBE在Bi_2Se_3薄膜上外延出了高質(zhì)量的NaCl-type的SnSe薄膜,確定了NaCl-type的SnSe薄膜的生長動力學(xué)條件。結(jié)合第一性原理計算和ARPES結(jié)果,我們首次確定了NaCl-type的SnSe是一種新的拓撲晶體絕緣體。(2)采用MBE的生長方式,我們在單層的Graphene上生長出了高質(zhì)量的(Bi1-xInx)2Se3(0≤x≤1)薄膜。并對這種體系進行了詳細的變層厚的ARPES研究,給出了這個體系的相變點:拓撲相變點在5%到9%之間,當(dāng)摻In量5%時,(Bi1-xInx)2Se3體系屬于拓撲非平庸態(tài);當(dāng)摻In量9%時,(Bi1-xInx)2Se3體系屬于拓撲平庸態(tài)。通過對ARPES結(jié)果的分析,我們首次證實:當(dāng)In摻雜到Bi_2Se_3體系中時,體系的體態(tài)能隙減小,體態(tài)能隙的減小會造成表面態(tài)的穿透深度增加,當(dāng)體態(tài)能隙減小到一定程度,表面態(tài)的穿透深度足夠深時,上下表面態(tài)就可以發(fā)生耦合,Dirac型表面態(tài)在發(fā)生拓撲相變之前打開能隙。另外,我們在α-In2Se3(厚度小于4QL)和Graphene的范德瓦爾斯異質(zhì)結(jié)中發(fā)現(xiàn)了很強的能帶調(diào)控效應(yīng),我們推測這種調(diào)控的能帶屬于超晶格Dirac點。為了證明這種猜測,我們正在做理論模擬。(3)我們采用MBE在高阻STO(111)面上生長出了高質(zhì)量的Bi_2Se_3薄膜,并對Bi_2Se_3薄膜進行了變層厚的熱電輸運的測量。我們發(fā)現(xiàn)Bi_2Se_3薄膜的熱電勢的絕對值以及功率因子隨層厚的增加而增加。我們希望跟理論模擬結(jié)合給出一種能夠繼續(xù)提高像Bi_2Se_3、Sb2Te3等拓撲絕緣體材料的熱電性質(zhì)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，

本文編號：2504581