  Topological states emerge at the boundary of solids as a consequence of the
nontrivial topology of the bulk. Recently, theory predicts a topological edge
state on single layer transition metal dichalcogenides with 1T' structure.
However, its existence still lacks experimental proof. Here, we report the
direct observations of the topological states at the step edge of WTe2 by
spectroscopic-imaging scanning tunneling microscopy. A one-dimensional
electronic state residing at the step edge of WTe2 is observed, which has a
spatial extension of about 2.5 nm. First principles calculations rigorously
verify the edge state has a topological origin, and its topological nature is
unaffected by the presence of the substrate. Our study supports the existence
of topological edge states in 1T'-WTe2, which may envision in-depth study of
its topological physics and device applications.
