1D edge state in single-bilayer Bi islands on the surface of bulk Bi, from Ref. [22]. (a) Schematics of Bi-bilayer’s atomic structure. Two types of edges are marked by red and blue lines, respectively. (b) STS of type-A and type-B edges, as well as of the terrace. (c) Quasi-particle interference within the edge channel. Two branches were observed: q₁ and q₂ come from the 1D edge state and 2D surface state, respectively. (d) Schematic of the band dispersion for the Bi bilayer on bulk Bi(111). The grey region represents the projected Bi(111) surface state continuum in the direction parallel to the 1D edge state. E₁ and E₂ indicate the peak positions in panel (b).