The energy spectrum of a finite chain (L = 64). The parameters are chosen as: (a) Δ = 0.2t, η = 0.1, t_A = 0, t_B = 0; (b) Δ = 0.1t, η = 0.2, t_A = 0.1t, t_B = −0.1t; (c) Δ = 0.2t, η = 0.1, t_A = 0.1t, t_B = 0.1t, respectively. The two middle eigenvalues are plotted in green (blue) while other energy eigenvalues are in red. The zero energy modes emerge in the topological region.