Instabilities in quantum point contact structures

We discuss the appearance of strong nonlinearities including S-type negative differential conductance in the I– Vcharacteristics of quantum point contact (QPC) structures. Time-dependent measurements demonstrate that the highly nonlinear d.c. I– Vfeatures are associated with a temporal average of random telegraph switching (RTS) between different current levels. The RTS is only observed when the voltage across the device is such that the chemical potential on one side of the QPC is aligned with the bottom of a one-dimensional subband in the QPC. As the chemical potential is moved further into the subband, the switching behavior disappears until the next subband minimum is reached.