  1H-phase monolayer transition-metal dichalcogenides have spin-split
electronic band structures near the K(K') point due to strong spin-orbit
coupling and intrinsic inversion symmetry breaking. In case of the monolayer
MoX2 (X=S, Se, Te), the spin-split conduction bands cross near the K(K') point.
We show that the band crossing occurs not only along the high symmetry
directions, but also along arbitrary directions due to a mirror reflection
symmetry of the monolayer. As a result, n-doped monolayer MoX2 is a
two-dimensional type-II nodal-line material.
