中文摘要：

随着拓扑绝缘体的发现,材料拓扑物性的研究成为凝聚态物理研究的热点领域.本文基于第一性原理计算,研究了化合物Ge2X2Te5（X=Sb,Bi）的块体结构和二维单层和双层薄膜结构的拓扑物性,以及单双层薄膜在垂直方向单轴压力下的拓扑量子相变.研究发现,A型原子序列排列的这两种化合物都是拓扑绝缘体,其单层薄膜都是普通金属,而双层薄膜都是拓扑金属,单层和双层薄膜在单轴加压过程中都没有发生拓扑量子相变;这两种化合物的B型原子序列的晶体是普通绝缘体,其所对应的薄膜,Ge2Sb2Te5单层是普通金属,双层薄膜和Ge2Bi2Te5的单层和双层薄膜均为普通绝缘体,但是在单轴加压过程中B型原子序列所对应的单层和双层薄膜都转变为拓扑金属.

英文摘要：

Since the topological insulator was discovered, the investigation of topological properties has become the hot spot in condensed matter physics. In this paper, we study topological properties of chalcogenide compounds Ge2X2Te5 （X = Sb, Bi） crystals and their monolayer and bilayer films as well as the vertical uniaxial pressure induced topological quantum phase transitions in monolayer and bilayer films. The results show that for A-type crystal, the bulk structures of these two compounds are topological insulators, the monolayer structures of these two compounds are conventional metals, and bilayer structures are topological metals. There is no topological quantum phase transition in monolayer nor bilayer film under the uniaxial compression. While for B-type crystal, the bulk structures of these two compounds are conventional insulators, the monolayer Ge2Sb2Te5 is conventional metal, its bilayer structure as well as monolayer and bilayer of Ge2Bi2Te5 films is conventional insulator. All the B-type monolayer and bilayer films each undergo a topological quantum phase transition to the topological metals under the uniaxial compression.