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Abstract:
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 locate at opposite momenta. Spin-orbit coupling can open a
gap at these Dirac points, inside which gapless topological edge states
exists as the quantum spin Hall (QSH) effect, the 2D topological
insulator.
