Topological Insulator in Two-Dimensional SiGe Induced by Biaxial Tensile Strain

Abstract

Strain-engineered two-dimensional (2D) SiGe is predicted to be a topological insulator (TI) based on first-principle calculations. The dynamical and thermal stabilities were ascertained through phonon spectra and ab initio molecular dynamics simulations. 2D SiGe remains dynamically stable under tensile strains of 4 and 6%. A band inversion was observed at the Γ-point with a band gap of 25 meV for 6% strain due to spin-orbit coupling interactions. Nontrivial of the TI phase was determined by its topological invariant (υ = 1). For SiGe nanoribbon with edge states, the valence band and conduction band cross at the Γ-point to create a topologically protected Dirac cone inside the bulk gap. We found that hexagonal boron nitride (h-BN) with high dielectric constant and band gap can be a very stable support to experimentally fabricate 2D SiGe as the h-BN layer does not alter its nontrivial topological character. Unlike other heavy-metal-based 2D systems, because SiGe has a sufficiently large gap, it can be utilized for spintronics and quantum spin Hall-based applications under ambient condition.