(a) Energy spectrum vs. the disorder strength parameter L_r. The red line marks the topological non-trivial gap which closes gradually as L_r increases. The states inside the gap are localized on the edges. (b) The computed local Chern numbers as a function of frequency for L_r = 0.1, which is marked by the dotted line in panel (a). In the gap region, the local Chern number is close to −1. (c) The field pattern of an edge state in the gap marked by the arrow in (b). (d) The computational domain is a 9 × 9 finite-sized sample. The red/blue/green highlights the 3 sectors used in the local Chern number computation. (e) The edge state pattern of a larger sample with 15 rows by 15 columns for L_r= 0.1. (f) The one-way propagating edge wave in a sample with an inserted defect.