We studied the square-octagonal lattice of the transition metal dichalcogenide MX2 (with M=Mo, W; X=S, Se and Te), as an isomer of the normal hexagonal compound of MX2. By band structure calculations, we observe the graphene-like Dirac band structure in a rectangular lattice of MX2 with nonsymmorphic space group symmetry. Two bands with van Hove singularity points cross each at the Fermi energy, leading to two Dirac cones that locates at opposite momenta. Spin-orbit coupling can open a nontrivial gap at these Dirac points and induce the quantum spin Hall (QSH) phase, the 2D topological insulator. Here, square-octagonal MX2 structures realize the interesting graphene physics, such as Dirac bands and QSH effect, in the transition metal dichalcogenides.
@article{arxiv.1503.08460,
title = {Graphene-like Dirac states and Quantum Spin Hall Insulators in the square-octagonal MX2 (M=Mo, W; X=S, Se, Te) Isomers},
author = {Yan Sun and Claudia Felser and Binghai Yan},
journal= {arXiv preprint arXiv:1503.08460},
year = {2015}
}