  Quantum spin Hall (QSH) effect is an intriguing phenomenon arising from the
helical edge states in two-dimensional topological insulators. We use molecular
beam epitaxy (MBE) to prepare FeSe films with atomically sharp nematic domain
boundaries, where tensile strains, nematicity suppression and topological band
inversion are simultaneously achieved. Using scanning tunneling microscopy
(STM), we observe edge states at the Fermi level that spatially distribute as
two distinct strips in the vicinity of the domain boundaries. At the endpoint
of the boundaries, a bound state at the Fermi level is further observed. The
topological origin of the edge states is supported by density functional theory
calculations. Our findings not only demonstrate a candidate for QSH states, but
also provide a new pathway to realize topological superconductivity in a
single-component film.
