Abstract
Quantum spin Hall (QSH) insulators feature edge states that topologically protected from backscattering. However, the major obstacles to application for QSH effect are the lack of suitable QSH insulators with a large bulk gap. Based on first-principles calculations, we predict a class of large-gap QSH insulators in ethynyl-derivative functionalized stanene (SnC2X; X = H, F, Cl, Br, I), allowing for viable applications at room temperature. Noticeably, the SnC2Cl, SnC2Br, and SnC2I are QSH insulators with a bulk gap of ~0.2 eV, while the SnC2H and SnC2F can be transformed into QSH insulator under the tensile strains. A single pair of topologically protected helical edge states is established for the edge of these systems with the Dirac point locating at the bulk gap, and their QSH states are confirmed with topological invariant Z2 = 1. The films on BN substrate also maintain a nontrivial large-gap QSH effect, which harbors a Dirac cone lying within the band gap. These findings may shed new light in future design and fabrication of large-gap QSH insulators based on two-dimensional honeycomb lattices in spintronics.
Highlights
A good Quantum spin Hall (QSH) insulator should be synthesized and have a large bulk band gap to realize the spin transport at high temperatures
GeCH3 film has been synthesized in recent work[27]. This raises an interesting question: can the methyl be applied to stabilize group IV and V films, and whether their band gap can be enhanced significantly in QSH phase? Motivated by recent works on stanene by zhang et al.[17], in our previous works[28], we have found that the organic molecule ethynyl (C2H) can be applied to stabilize stanene by decoration on its surface, and its band gap in TI states reaches up to 0.3 eV
The SnC2Cl, SnC2Br, and SnC2I are all QSH insulators with a bulk gap of ~ 0.2 eV, while the SnC2H and SnC2F can be transformed into QSH insulator under the tensile strains
Summary
Run-wu Zhang[1], Chang-wen Zhang[1], Wei-xiao Ji1, Sheng-shi Li1,2, Shi-shen Yan[2], Shu-jun Hu2, Ping Li1, Pei-ji Wang1 & Feng Li1. The films on BN substrate maintain a nontrivial large-gap QSH effect, which harbors a Dirac cone lying within the band gap These findings may shed new light in future design and fabrication of large-gap QSH insulators based on two-dimensional honeycomb lattices in spintronics. An approach to design a large-gap QSH state on a semiconductor surface by a substrate orbital filtering process is proposed[23,24]. These large-gap QSH insulators are essential for realizing many exotic phenomena and for fabricating new quantum devices that can operate at room temperature
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