Modal analysis of transport through quantum point contacts using realistic potentials

We have studied conduction through quantum point contacts using a coupled-mode analysis and realistic potentials. Disorder causes transport to be strongly nonadiabatic with rapid intermode scattering. The conductance can remain well quantized because of the predominantly forward nature of the scattering. Resonances in the channel lead to strong indirect backscattering that cannot be described by the Born approximation. This degrades quantization in point contacts and reduces the mobility of narrow wires.