Low-buckled silicene is a prototypical quantum spin Hall insulator with thetopological quantum phase transition controlled by an out-of-plane electricfield. We show that this field-induced electronic transition can be furthertuned by an in-plane hydrostatic biaxial strain $\varepsilon$, owing to thecurvature-dependent spin-orbit coupling (SOC): There is a $Z_2$ = 1 topologicalinsulator phase for biaxial strain $|\varepsilon|$ smaller than 0.07, and theband gap can be tuned from 0.7 meV for $\varepsilon = +0.07$ up to a fourfold3.0 meV for $\varepsilon = -0.07$. First-principles calculations also show thatthe critical field strength $E_c$ can be tuned by more than 113\%, with theabsolute values nearly 10 times stronger than the theoretical predictions basedon a tight-binding model. The buckling structure of the honeycomb lattice thusenhances the tunability of both the quantum phase transition and theSOC-induced band gap, which are crucial for the design of topologicalfield-effect transistors based on two-dimensional materials.
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