Hall electric field-dependent broadening of extended state bands in Landau levels and breakdown of the quantum Hall effect

Current dependence of activation energy has been measured in the diagonal resistance of two standard butterfly-type Hall bars and a butterfly-type Hall bar with a short and narrow channel in the central part made from GaAs/AlGaAs heterostructures. The activation energy E-A in each sample decreases with increasing current and is expressed by E-A = E-A0 - ael(B)F(H) where E-A0 = hw(C)/2 at the plateau center for i = 2 and 4, a = 38 +/- 8, l(B) is the radius of the ground Landau orbit and F-H the Hall electric field. The result suggests that broadening of extended state bands in Landau levels due to the Hall electric field give rise to the magnetic field dependence of the critical Hall electric field. F-cr infinity B-3/2, obtained in various butterfly-type Hall bars. (C) 1998 Elsevier Science B.V. All rights reserved.