Edge modes in zigzag and armchair ribbons of monolayer MoS₂

We explore the electronic structure, orbital character and topological aspect of a monolayer MoS₂ nanoribbon using tight-binding (TB) and low-energy ([Formula: see text]) models. We obtain a mid-gap edge mode in the zigzag ribbon of monolayer MoS₂, which can be traced back to the topological properties of the bulk band structure. Monolayer MoS₂ can be considered as a valley Hall insulator. The boundary conditions at armchair edges mix the valleys on the edges, and a gap is induced in the edge modes. The spin-orbit coupling in the valence band reduces the hybridization of the bulk states.