First-principles study on the uniaxial pressure induced topological quantum phase transitions of Ge2X2Te5 (X =Sb, Bi) thin films

Abstract

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.