Strain and chemical function decoration induced quantum spin Hall effect in 2D silicene and Sn film

• The inverted band order can be obtained with applying external strain.
• Band gaps of TIs can be enhanced by external strain.
• Quantum phase transition is observed under a critical strain for XSi and XSn.

The topological properties of silicene and Sn film decorated with chemical functional groups (–H, –F, –Cl, –Br, –I) are investigated by the first-principle calculations. It is found that Sn films decorated with F, Cl, Br and I are topological insulators with sizable gap while the other combinations are normal insulators. The phase transition of X decorated silicene and Sn film was investigated by applying external strain. Our results pointed out that the normal insulators can transform into topological insulators with sizable gap under critical strain. The research provided new routes to design 2D topological insulator with sizable gap which has wide applications in next-generation spintronics devices.