Phase diagram for the ladder model of the dimerized Kitaev chains as a function of the pairing amplitude and the chemical potential with chains numbers n along the y axis. The energy unit is t_x, and we have taken θ = 0, |Δ_x| = |Δ_y| = Δ, t_y = 0.3t_x, and η = 0.3t_x. The integer numbers in the figure represent the ℤ index. The white dashed lines guide the value of Δ = 0.1t_x. (a) n = 2; (b) n = 3; (c) n = 4; (d) n = 5; (e) n = 6; (f) n = 7.