(c) Resonant transmission and reflection of edge channels. The electrostatic potential in a point contacthas a saddle shape (cf. Fig. 103), due to the combination of the lateral confinement and the potential barrier. The height of the barrier can be adjusted by means of the gate voltage. An edge state with a guiding center energy below the barrier height is a bound state in the cavity formed by two opposite point contacts, as is illustrated in Fig. 106a. Tunneling of edge channels through the cavity via this bound state occurs with transmission probability TAB, which for a singe edge channel is given by474,498