THE DECAY OF INDUCED EDDY CURRENTS IN A 2-DIMENSIONAL ELECTRON-SYSTEM

Large long-lived eddy currents are induced in a two-dimensional electron system as the magnetic field is swept through the almost dissipationless states associated with the quantum Hall effect. We have measured the temperature dependence of the decay times of these currents in a GaAs/AlGaAs single heterojunction, using a torque magnetometer at dilution refrigerator temperatures. At Landau-level filing factor nu = 4, the decay time is less than a minute at T = 40 mK, whereas at nu = 1 and 2 we observe a decay lime of about 4 hours which follows a short initial decay of the order of minutes. We discuss the possible mechanisms for decay of the currents and conclude that the energy is stored predominantly in the Hall electric field between the edge and the centre of the sample. At T = 40 mK we estimate a 2D resistivity of the order of 10(-14) Omega/square for nu = 1 and 2 and 10(-11) Omega/square for nu = 4.