Spatial distribution of nonequilibrium electrons in quantum Hall devices: Imaging via cyclotron emission

Images of the spatial distribution of nonequilibrium electrons are studied in a wide quantum Hall effect (QHE) Hall bar (ν=2) by detecting the local profile of the cyclotron radiation with an improved spatial resolution of 50μm for the radiation wavelength of λ=120μm. The experiments, along with conventional studies of voltage distribution via voltage probes, reveal the generation of nonequilibrium carriers at the diagonally opposite corners of Hall bars (hot spots) at low current levels (below 80μA), as well as the occurrence of additional generation of nonequilibrium carriers at the corner opposite to the hot spot on the side of the source contact at higher currents (above 80μA). The experimental findings are consistently interpreted in terms of earlier models of the electron dynamics around current contacts, providing support to the model of bootstrap-type electron heating for the breakdown of the QHE.