Effects of accidental microconstriction on the quantized conductance in long wires

TL;DR

This paper investigates how accidental microconstrictions caused by donor clustering or lithographic inaccuracies can restore quantized conductance plateaux in long quantum wires, which are otherwise degraded by potential fluctuations.

Contribution

It demonstrates that microconstrictions can recover quantized conductance in long wires affected by potential fluctuations, providing insight into conductance behavior under realistic imperfections.

Findings

Microconstrictions restore conductance quantization.

Potential fluctuations cause conductance oscillations.

Lithographic inaccuracies have similar effects.

Abstract

We have investigated the conductance of long quantum wires formed in GaAs/AlGaAs heterostructures. Using realistic fluctuation potentials from donor layers we have simulated numerically the conductance of four different kinds of wires. While ideal wires show perfect quantization, potential fluctuations from random donors may give rise to strong conductance oscillations and degradation of the quantization plateaux. Statistically there is always the possibility of having large fluctuations in a sample that may effectively act as a microconstriction. We therefore introduce microconstrictions in the wires by occasional clustering of donors. These microconstrictions are found to restore the quantized plateaux. A similar effect is found for accidental lithographic inaccuracies.