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.

Figure 1

Resistance as a function of temperature for the mesoscopic sample prior to illumination. Increasing gate voltage shows weaker dependence signifying the tunneling regime. The inset shows the temperature dependence of the mesoscopic sample following illumination. More negative gate voltages were required to observe an activated dependence.

Figure 2

(a)–(c) Conductance evolution of the mesoscopic sample whilst subject to ultra-low intensity illumination. The three segments are from a single experimental run each spanning an order of magnitude in units of $e^2∕h$. (d) Conductance evolution of an independent sample defined by a split-gate technique.

Figure 3

Statistics at $4.2\mathrm{K}$ of single-photon induced conductance steps for three different source-drain voltages. Also shown are the statistics of single-photon induced conductance steps in a sample defined with split-gates. Solid lines are fit to the data with slopes $\lambda =1.0$, 1.12, and 1.04 from top to bottom.