A first-principles investigation of pressure induced topological phase transitions in half-Heusler AgSrBi

Abstract

Topological insulators (TI) are materials with novel quantum states and exhibit a bulk insulating gap, while their edge/surface is conducting. This has been extensively explored in several half-Heusler (HH) compounds. In the present work we employ first-principles calculations based on density functional theory to perform thorough investigations of pressure induced topological phase transitions (TPT) in HH AgSrBi which belongs to the F3m space group. AgSrBi is intrinsically semi-metallic in nature which under isotropic pressure exhibits a semi-metal to trivial insulator transition while retaining the cubic symmetry. Also, we observe that this phase of AgSrBi is dynamically stable at extreme pressures as high as ∼23.5 GPa. However, on breaking the cubic symmetry we observe the much desired TI nature after a non-trivial phase transition from a semi-metal to TI. We also explore the effect of lowering the crystal symmetry along with dimensional confinement in realizing a two-dimensional (2D) TI, AgSrBi, which is done by cleaving the [111] crystal plane. We perform a qualitative analysis of the electronic properties to understand the origin of this non-trivial behavior in the bulk and 2D phases of AgSrBi. This is accompanied by a quantitative analysis of the invariants and surface/edge state spectra, which further confirms the TI nature of AgSrBi. Hence, we propose the bulk as well as 2D phase of AgSrBi as a dynamically stable TI which can be used as ultra-thin films for thermoelectric, spintronic and nanoelectronic applications.