Strain-tunable topological quantum phase transition in buckled honeycomb lattices

Low-buckled silicene is a prototypical quantum spin Hall insulator with the topological quantum phase transition controlled by an out-of-plane electric field. We show that this field-induced electronic transition can be further tuned by an in-plane biaxial strain epsilon, owing to the curvaturedependent spin-orbit coupling (SOC): There is a Z(2) = 1 topological insulator phase for biaxial strain vertical bar epsilon vertical bar smaller than 0.07, and the band gap can be tuned from 0.7 meV for epsilon = +0.07 up to 3.0 meV for epsilon = -0.07. First-principles calculations also show that the critical field strength E-c can be tuned by more than 113%, with the absolute values nearly 10 times stronger than the theoretical predictions based on a tight-binding model. The buckling structure of the honeycomb lattice thus enhances the tunability of both the quantum phase transition and the SOC-induced band gap, which are crucial for the design of topological field-effect transistors based on two-dimensional materials. (c) 2015 AIP Publishing LLC.