Supercritical nondissipative currents in quantum Hallsystems

摘要

We have studied the electric response of quantum Hall systems tosub- and supercritical nanosecond voltage pulses. We found that thebreakdown of the QHE is suppressed on time scales up to a few nanoseconds,even for supercritical voltages and currents being more than 3 times higherthan the dc-breakdown value. The electric response of the sample is mainlydetermined by processes during the pulse, but not by the average current.Further, there is no accumulative effect of dissipation during the pulse pauseslonger than a few nanoseconds. Thus, the relaxation times trel from thedissipative to the QH state are shorter than a few ns and of the same order asthe excitation times texc. Applying a drift model, we estimate inelasticscattering lengths which are in the micrometer range and conclude that inter-Landau-level transitions, enforced by local impurity potential fluctuations,can explain these time and length scales. A comparison of the data obtained atsamples with Hall and Corbino geometry allows us to discuss the role of bulkand edge effects near the breakdown of the QHE. At some Corbino devicesthe critical pulse width tpc was found to change nonlinearly and stepwise withthe average VSD values in Corbino devices at filling factor 2. We attribute thisbehaviour to an increasing number of discrete current filaments.[73.43.-f, 73.43.Jn, 73.20.Jc]