Quantum spin Hall effect in two-dimensional transition-metal dichalcogenide haeckelites

Based on first-principles calculations, we have found that a family of two-dimensional transition-metal dichalcogenide haeckelites with square-octagonal lattice M X-2-4-8 (M = Mo, W and X = S, Se and Te) can host quantum spin Hall effect. The phonon spectra indicate that they are dynamically stable, and the largest band gap is predicted to be around 54 meV. These will pave the way for potential applications of topological insulators. We have also established a simple tight-binding model on a squarelike lattice to achieve a topologically nontrivial quantum state, which extends the study from honeycomb lattice to squarelike lattice and broadens the promising topological material systems greatly.