Quantum Hall induced currents and the magnetoresistance of a quantum point contact

We report an investigation of quantum Hall induced currents by simultaneous measurements of their magnetic moment and their effect on the conductance of a quantum point contact (QPC). Correlation of features in the noise of the induced currents, caused by the breakdown of the quantum Hall effect, for the two types of measurements provides conclusive proof of the common origin of the two effects. Common features in the magnetic moment and QPC resistance at Landau-level filling factors nu = 1, 2 and 4 and their similar temperature and nonlinear sweep-rate dependences support this conclusion. In contrast, there is a distinct difference in the way the induced currents decay with time when the sweeping field halts at integer filling factor as detected by the two types of measurement. We attribute this difference to the fact that, while both effects are sensitive to the magnitude of the induced current, the QPC resistance is also sensitive to the proximity of the current to the QPC split gate, and we develop a model that describes semi-quantitatively the effects we observe. Although it is clearly demonstrated that induced currents affect the electrostatics of a QPC, the reverse effect, the QPC influencing the induced current, is not observed.