NONLINEAR BEHAVIOR IN THE MAGNETOTRANSPORT THROUGH CONTINUOUS GATE AND SPLIT GATE NANOSTRUCTURES

Quantum point contacts (QPCs), defined by surface gate technology, are increasingly featuring as basic building blocks of more sophisticated geometries such as coupled dot, single electron, and coherent wave de vices. For many of its potential roles the electron density within the QPC needs to be known accurately as a function of the voltage applied to the split gates that define the QPC within the two-dimensional ele ctron gas. A common characterization technique extracts the density fr om the positions of the conductance plateaus that result from the depo pulation of edge states as the gate voltage is swept at high magnetic fields. We study the high current breakdown of these plateaus and inve stigate the nonlinear current-voltage characteristics for both split g ate and continuous gate geometries. We demonstrate that the breakdown is not centred around the plateaus and that, unlike the breakdown of t he quantum Hall effect, a forward propagation mechanism needs to be co nsidered and indeed is the dominant process.