(color online) The influence of exchange field on edge states. (a) Energy gap as a function of the exchange field h ₁. It can be seen that the energy gap has a process from closing to opening. Energy spectrums corresponding to points A (b), B (c), and C (d) in panel (a) are plotted versus k _x (with ). The first three sub-bands are striped with red, green, and blue colors, respectively. The parameters used in the calculation are meV and l = 7.