BISTABILITY IN THE CURRENT-INDUCED BREAKDOWN OF THE QUANTUM HALL-EFFECT

The structure of the longitudinal resistance in the breakdown behaviour of the quantum Hall effect (QHE) of GaAs/AlGaAs heterostructures is studied at a temperature of about 100 mK using samples with a constricted current path. Time-resolved measurements on a sample with a 50 mum wide constriction show that the current-induced breakdown of the QHE evolves as a switching between at least two states, a non-dissipative one and a resistive one. The two states may coexist in some region of magnetic field and sample current. This shows up in the time behaviour of the longitudinal voltage, which is time-distributed in a statistical manner. Increasing the sample current at fixed magnetic field increases the time the current carriers stay in the resistive state rho(dis) until at high enough currents all backswitching into the non-dissipative state is suppressed. At filling factors nu less-than-or-equal-to 2, the resistivity rho(dis), increases linearly with the difference DELTAnu = nu - nu(i) with nu(i) = 2. The corresponding voltages are found to be less than homega(c)/eBAR at all sample currents, contrary to results of Cage et al. For filling factors with nu greater-than-or-equal-to 2 the sample shows no similar effect. The results will be discussed within the framework of several existing models for the breakdown behaviour of the QHE.