CONDUCTIVITY PEAKS IN THE QUANTUM HALL REGIME - BROADENING WITH TEMPERATURE, CURRENT, AND FREQUENCY

We argue that it is hopping transport that is responsible for broadeni ng of the sigma(xx) peaks in low-mobility samples. Explicit expression s for the width DELTAnu of a peak as a function of the temperature T, current J, and frequency omega are found. It is shown that DELTAnu gro ws with T as (T/T1)kappa, where kappa is the inverse localization-leng th exponent. The current J is shown to act like an effective temperatu re T(eff)(J) is-proportional-to j1/2 if T(eff)(J) much greater than T. Broadening of the ohmic ac-conductivity peaks with frequency omega is found to be determined by the effective temperature T(eff)(omega) alm ost-equal-to HomegaBAR/k(B).