Gate-controlled current distribution on double-bridge quantum Hall conductors

Abstract

We investigated the local potential distribution over gated double-bridge structures patterned on GaAs/GaAlAs heterostructures. The current and potential distribution over the gated double-bridge devices was measured for several sets of filling factors below the two gates and in the ungated region. The fractions of the Hall voltage and the bridge currents experimentally obtained for both bridges correspond exactly to the values predicted by model calculations. Depending on the choice of the filling factor distribution, particular sequences of voltage steps across the bridges can be generated. This might be of some interest for metrological applications. We show that the current and voltage distribution for the double-gate device can be calculated using the edge-current picture. However, it is also shown that exactly the same results can be obtained using a local model in which edge currents are not considered. This has consequences concerning the open question of the extent to which the existence of edge currents in quantizing magnetic fields affects magnetotransport data at integer filling factors.

Gate-voltage-induced realization of different rational fractions ofh/e2at fixed values of current and magnetic field

“…As we have shown in a previous paper [6], applying either the edge channel model of the QHE or a local transport model (considering quantized Hall voltages, vanishing longitudinal voltages and applying Kirchhoff's laws) to the structures in Fig. 1 leads to the same results for the potential distribution on the sample edges.…”

“…between contacts 3 and B) because the longitudinal voltages vanish in the quantum Hall regime. Measurement results on a sample of type A for the special case of filling factors ν G1 = ν 0 /2 (ν 0 = 2, 4, 6) have been published in a previous paper [6]. The measurements shown in figs.…”

“…However, an explanation for the observed behavior of R BC can be achieved by extending the local transport model used in [6] to the case of non-integer filing factors below one gate. In this model the filling factor dependence of the Hall voltage…”