An ab initio approach to understand the structural, mechanical, thermophysical, electronic, and optical properties of topological insulators AMg2Bi2 (A = Ca, Yb)

Abstract

The exceptional thermoelectric and magnetic properties exhibited by thermoelectric materials are widely recognized. In contrast, the recent discovery of non-trivial topological phases in several thermoelectric materials, such as AMg₂Bi₂ (A = Ca, Yb), has introduced novel avenues for further research. AMg₂Bi₂ is a strong Z₂ topological insulator due to its narrow band gap and topological surface electronic states. By employing the generalized gradient approximation (GGA) within the density functional theory (DFT), we have thoroughly investigated the mechanical, electronic, optical, and elastic characteristics of AMg₂Bi₂. The result indicates that the substance is soft, brittle, mechanically stable, and moderately machinable. Furthermore, the results indicate that a considerable quantity of covalent and metallic bonding is present in the crystal structure. A relatively low Debye temperature implies that the substance being studied is soft and has weakly bonded atoms. In the presence of spin-orbit coupling (SOC), electronic band structure calculations reveal the characteristics of topological insulators with a Dirac cone and band inversion observed at the Γ-point. Additionally, the optical properties of AMg₂Bi₂ at different photon energies are investigated. AMg₂Bi₂ exhibits a significant refractive index in the visible spectrum. Both compounds are very capable of effectively absorbing low-energy UV light. However, they exhibit exceptional reflective properties when exposed to high-energy UV radiation. All of these optical properties can be used in optoelectronic device applications.