Strain-Induced Topological Insulator in Methyl-Decorated SiGe Films

Since the discovery of topological insulators (TIs), there has been much research into prediction and experimentally discovering distinct classes of these materials, in which the bulk insulating but helical edge states are conducting in the absence of magnetic field. Herein, using first-principle calculations along with tight-binding model, methyl-decorated SiGe film is shown to undergo a topological phase transition under external tensile strain. The band gap can be tuned by the tensile strain, and at critical strain (ε = 8%) at Γ-point opens a gap Eg = 0.35 eV due to band inversion. The nonzero topological invariant and helical edge states are further confirmed by topological invariant, Z2 = 1, for stretched SiGeCH3. Thus, a large energy gap induced by spin–orbit coupling and tensile strain indicates that methyl-decorated SiGe film is quite promising to design two-dimensional TIs materials for practical application. Moreover, for design and fabrication of topological electronic devices, we propose a bilayer of hexagonal boron nitride as suitable substrate for supporting SiGeCH3 film without perturbing the nontrivial topology