GATE-CONTROLLED CURRENT DISTRIBUTION ON DOUBLE-BRIDGE QUANTUM HALL CONDUCTORS

We investigated the local potential distribution over gated double-bri dge structures patterned on GaAs/GaAlAs heterostructures. The current and potential distribution over the gated double-bridge devices was me asured for several sets of filling factors below the two gates and in the ungated region. The fractions of the Hall voltage and the bridge c urrents experimentally obtained for both bridges correspond exactly to the values predicted by model calculations. Depending on the choice o f the filling factor distribution, particular sequences of voltage ste ps across the bridges can be generated. This might be of some interest for metrological applications. We show that the current and voltage d istribution for the double-gate device can be calculated using the edg e-current picture. However, it is also shown that exactly the same res ults can be obtained using a local model in which edge currents are no t considered. This has consequences concerning the open question of th e extent to which the existence of edge currents in quantizing magneti c fields affects magnetotransport data at integer filling factors.