Spatially resolved measurements of hot-electron generation and relaxation at the breakdown of the quantum Hall effect

We have measured the dissipative resistivity of quantum Hall conductors as a function of the distance from the electron injection. The injection of el ectrons into constrictions at supercritical current levels allowed to monit or the evolution of the breakdown along the drift direction. After a smooth increase, an avalanche-like growth of the resistivity occurs. Drastic chan ges of the resistivity profiles with the applied current near the breakdown value were observed and are attributed to tunneling between Landau levels. By injecting hot electrons from constrictions into a sample region at subc ritical currents, the relaxation process was analyzed. The inelastic relaxa tion lengths agreed with the elastic mean free path within 10%, indicating the importance of scattering at impurity potentials. (C) 1999 Elsevier Scie nce B.V. All rights reserved.