(color online) (a) Wave function distributions of states A and B marked in Fig. 2(g) for the HgTe cylinder, where the gate voltage is applied to the 40st lattice site (see the inset), (b) the wave function distributions from the 35st to 45st lattice, (c) the wave function distributions of the states C and D labeled in Fig. 2(h) for a HgTe nanoribbon in open boundary conditions, while without any gate voltage, and the size of the sample is shown in the inset.