Unexpected features of branched flow through high-mobility two-dimensional electron gases

TL;DR

This study investigates electron flow in high-mobility GaAs/AlGaAs 2DEGs, revealing unexpected stability of branched flow and suppression of interference fringes, which challenge existing understanding of disorder effects in these systems.

Contribution

It uncovers novel phenomena in high-mobility 2DEGs, including the near absence of impurity scattering and the stability of branched flow against initial condition variations.

Findings

Suppression of quantum interference fringes in high-mobility samples

Branched flow remains stable despite changes in initial electron conditions

Electron flow branches are straight over distances proportional to mean free path

Abstract

GaAs-based two-dimensional electron gases (2DEGs) show a wealth of remarkable electronic states, and serve as the basis for fast transistors, research on electrons in nanostructures, and prototypes of quantum-computing schemes. All these uses depend on the extremely low levels of disorder in GaAs 2DEGs, with low-temperature mean free paths ranging from microns to hundreds of microns. Here we study how disorder affects the spatial structure of electron transport by imaging electron flow in three different GaAs/AlGaAs 2DEGs, whose mobilities range over an order of magnitude. As expected, electrons flow along narrow branches that we find remain straight over a distance roughly proportional to the mean free path. We also observe two unanticipated phenomena in high-mobility samples. In our highest-mobility sample we observe an almost complete absence of sharp impurity or defect scattering, indicated by the complete suppression of quantum coherent interference fringes. Also, branched flow through the chaotic potential of a high-mobility sample remains stable to significant changes to the initial conditions of injected electrons.