  We performed noise measurements in a two-dimensional electron gas to
investigate the nonequilibrium quantum Hall effect (QHE) state. While excess
noise is perfectly suppressed around the zero-biased QHE state reflecting the
dissipationless electron transport of the QHE state, considerable finite excess
noise is observed in the breakdown regime of the QHE. The noise temperature
deduced from the excess noise is found to be of the same order as the energy
gap between the highest occupied Landau level and the lowest empty one.
Moreover, unexpected finite excess noise is observed at a finite source-drain
bias voltagesmaller than the onset voltage of the QHE breakdown, which
indicates finite dissipation in the QHE state and may be related to the
prebreakdown of the QHE.
