Photon-induced conductance steps and in situ modulation of disorder in mesoscopic electron systems

We study the conductance of a disordered two-dimensional electron system (2DES) at a mesoscopic length scale in which the localization length can be controlled and varied during an experiment. The localization is induced by a quantum dot layer adjacent to the 2DES, whose charge occupancy can be controlled optically. Under illumination the 2DES conductance increases in sharp steps due to the discharging of individual dots by single photo-excited holes. As the 2DES localization length increases, electron transport evolves from hopping through a small network to direct tunneling across the sample.