B. Selective population and detecti

B. Selective population and detection of edge channelsThe absence of local equilibrium at the current or voltage contacts leads to anomalies in the quantum Hall effect, unless the contacts are ideal (in the sense that each edge channel at the Fermi level is transmitted through the contact with probability 1). Ideal versus disordered contacts are dealt with in Sections IV.B.1 and IV.B.2. A quantum point contact can be seen as an extreme example of a disordered contact, as discussed in Section IV.B.3. Anomalies in the Shubnikov-De Haas effect due to the absence of local equilibrium are the subject of Section IV.B.4.