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%Studying the finite size properties of two-dimensional crystalline materials is a basic and interesting topic to be surveyed.
We explore the electronic structure, orbital character and topological aspect of a monolayer MoS$_2$ nanoribbon using tight-binding (TB) and low-energy (${\bm k}\cdot{\bm p} $) models. We obtain a mid gap edge mode in a zigzag ribbon, which can be traced back to the topological properties of the bulk band structure. MoS$_2$ can be considered a valley Hall insulator.
%The modes reveal a weak topological state which is {\it valley quantum Hall phase} of the system when chemical potential intersects those boundary modes. The hotspots of the Berry curvature around K-point indicate that the low-energy model around the K-point could capture the topological phase resulted from of the full TB model in the whole Brillioun Zone.
The boundary conditions at armchair edges mix the valleys, and a gap is induced in the edge modes. The spin-orbit coupling in the valence band reduces the hybridization.
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