Hysteretic effects in lateral nanostructures caused by long-lived quantum-Hall eddy currents

Coulomb blockade studies of lateral quantum dots and measurements of the quantised conductance of quantum point contacts, in high magnetic fields, reveal novel features which are hysteretic in magnetic-field sweep direction. These features are associated with long-lived eddy currents, induced in the 2D electron gas leads in these devices as the magnetic field sweeps and the 2DEG enters the quantum Hall effect state. Torsion-balance magnetometry measurements confirm the presence of these induced currents, and their influence on the nanostructures. The decay of the eddy currents, after the magnetic field sweep is stopped, exhibits two distinct regimes: a fast initial exponential decay followed by a much longer power-law decay in which the size of the eddy current falls typically to 60% of its original value in one day. The interpretation of these observations is that the Coulomb blockade and quantum point contact devices are influenced by the local Hall potential at the edges of the 2DEG leads. The Hall potential changes the local chemical potential of the leads, and hence the properties of the devices, in a manner which reverses when the field sweep direction is reversed.