Spatially probed electron-electron scattering in a two-dimensional electron gas

Using scanning gate microscopy (SGM), we probe the scattering between a beam of electrons and a two-dimensional electron gas (2DEG) as a function of the beam's injection energy, and distance from the injection point. At low injection energies, we find electrons in the beam scatter by small angles, as has been previously observed. At high injection energies, we find a surprising result: placing the SGM tip where it backscatters electrons increases the differential conductance through the system. This effect is explained by a nonequilibrium distribution of electrons in a localized region of 2DEG near the injection point. Our data indicate that the spatial extent of this highly nonequilibrium distribution is within similar to 1 mu m of the injection point. We approximate the nonequilibrium region as having an effective temperature that depends linearly upon injection energy.