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

The structure of the longitudinal resistance in the breakdown behaviou r of the quantum Hall effect (QHE) of GaAs/AlGaAs heterostructures is studied at a temperature of about 100 mK using samples with a constric ted 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 statistic al manner. Increasing the sample current at fixed magnetic field incre ases the time the current carriers stay in the resistive state rho(dis ) until at high enough currents all backswitching into the non-dissipa tive state is suppressed. At filling factors nu less-than-or-equal-to 2, the resistivity rho(dis), increases linearly with the difference DE LTAnu = nu - nu(i) with nu(i) = 2. The corresponding voltages are foun d to be less than homega(c)/eBAR at all sample currents, contrary to r esults of Cage et al. For filling factors with nu greater-than-or-equa l-to 2 the sample shows no similar effect. The results will be discuss ed within the framework of several existing models for the breakdown b ehaviour of the QHE.