Nonlinear transport properties of samples with inner current contacts in quantum Hall regime

We have performed transport: measurements in the quantum Hall regime using Hall-bar sample with inner current contact. In the plateau of the integer quantum Hall effect, we found a region where voltage drop along the channel V-x is negative. Considering the suppression of scattering between inner and outer edge states at low temperature, this negative voltage can be explained as a result of non-equilibrium distribution of electrons injected from the inner current contact. In addition, drastic frequency dependence of the negative resistance was found at very low frequency. (C) 1998 Elsevier Science B.V. All rights reserved.