Tunable nonlinear current-voltage characteristic in four-terminal ballistic nano-junctions

We report on low temperature (4.2K - 140K) measurements of four-terminal ballistic nano-junctions, etched on a two-dimensional electron gas confined in an InGaAs/InAlAs heterostructure. A symmetry-breaking artificial scatterer is introduced in the center of the junctions. The geometry of the junctions and scatterers is inspired by a recent theoretical work by Fleischmann and Geisel (R. Fleischmann and T. Geisel, Phys. Rev. Lett. 8,016804 (2002)). We measure the voltage V_LU generated between the upper and lower contacts when a current I_SD flows between the left and right contacts. We demonstrate that the shape, the amplitude and even the sign of the nonlinear V_LU(I_SD) characteristic can be tuned by applying voltage biases on side gates and/or illuminating the sample. The origin of this behavior is discussed using comparisons to Monte-Carlo (semiclassical) simulations of our devices.