Double-row transport in quantum wires of shallow confinement

The bifurcation of the electron system in a quantum wire has been observed in the form of the suppression and disappearance of the quantised conductance plateau at 2e2/h. We now present low-temperature transport measurements of a top-gated split-gate quantum wire that serve to further characterise this double-row régime of transport. A small distortion of the confinement caused by asymmetrical biasing of the split gates gives rise to a radical change in the conductance characteristics of the wire, beginning with the introduction of a plateau at G=e2/h which rises to around 0.7×2e2/h with greater differential bias between the split gates. DC source–drain bias measurements in this régime show a split zero-bias peak at low conductances merging into a single peak around G=0.7×e2/h, which then persists up to the plateau at 4e2/h.