Ethynyl-functionalized stanene film: A promising candidate as large-gap quantum spin Hall insulator

Quantum spin Hall (QSH) effect is promising for achieving dissipationless transport devices which can be achieved only at extremely low temperature presently. The research for new large-gap QSH insulators is critical for their realistic applications at room temperature. Based on first-principles calculations, we propose a QSH insulator with a sizable bulk gap as large as ∼0.22 eV in stanene film functionalized with the organic molecule ethynyl (SnC₂H), whose topological electronic properties are highly tunable by the external strain. This large-gap is mainly due to the result of the strong spin-orbit coupling related to the p_xy orbitals at the Γ point of the honeycomb lattice, significantly different from that consisting of the p_z orbital as in free-standing group IV ones. The topological characteristic of SnC₂H film is confirmed by the Z₂ topological order and an explicit demonstration of the topological helical Dirac type edge states. The SnC₂H film on BN substrate is observed to support a nontrivial large-gap QSH, which harbors a Dirac cone lying within the band gap. Owing to their high structural stability, this two-dimensional large-gap QSH insulator is promising platforms for topological phenomena and new quantum devices operating at room temperature in spintronics.