High-current ballistic transport through variable-width constrictions in a high-mobility two-dimensional electron gas

The nonlinear variation of resistance with current for short constrictions in a two-dimensional electron gas has been experimentally established for currents up to ±100 μA. The nonlinear device characteristics persist over a wide range of constriction widths and thus are not related to quantized conductance effects. At low currents (≤∼15 μA), a significant decrease in the resistance is observed with respect to the zero-current value, contrary to the expectation that increased electron scattering should lead to a resistance rise. This is attributed to the lowering of a potential barrier in the constriction by the applied bias, leading to an increase in the effective conducting width. An analytical expression for this low-current phenomenon is derived and is shown to give reasonable agreement with the experimental observations.