  The low-temperature resistance of a conducting LaAlO3/SrTiO3 interface with a
10 nm thick LaAlO3 film decreases by more than 50% after illumination with
light of energy higher than the SrTiO3 band-gap. We explain our observations by
optical excitation of an additional high mobility electron channel, which is
spatially separated from the photo-excited holes. After illumination, we
measure a strongly non-linear Hall resistance which is governed by the
concentration and mobility of the photo-excited carriers. This can be explained
within a two-carrier model where illumination creates a high-mobility electron
channel in addition to a low-mobility electron channel which exists before
illumination.
