We present magnetoresistance measurements in an ${\mathrm{Al}}_{\mathrm{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As/GaAs heterojunction with a gate covering a small region of the sample. With this device the Landauer approach to the resistance can be directly studied. The two-dimensional electron gas preserved in the nondissipative quantum Hall regime acts as the ideal leads necessary in this approach. The behavior of the scattering region formed by the gated part in between the undisturbed parts (ideal leads) of the sample is investigated by application of different voltages to the gate. We measured the dependence of the device resistance on the gate voltage and the number of available channels within the ideal leads. It is found that a theory based on the classical drift of electrons along equipotential lines (trajectories) accompanied by two types of transitions (intra- and inter-Landau-level transitions) between them is able to explain the main features of experiments.

• Received 17 October 1988

DOI:https://doi.org/10.1103/PhysRevB.39.10892