Scanning gate imaging in confined geometries

TL;DR

This study uses scanning gate microscopy to explore how electron flow in confined geometries transitions through different regimes, revealing conditions under which observed branches reflect actual electron trajectories.

Contribution

It introduces a tunable method to investigate electron backscattering and flow regimes in confined geometries, supported by classical simulations.

Findings

Identified three distinct flow regimes in confined electron channels.

Demonstrated how conductance and branching behavior change with confinement.

Provided microscopic understanding of branch formation and disappearance.

Abstract

This article reports on tunable electron backscattering investigated with the biased tip of a scanning force microscope. Using a channel defined by a pair of Schottky gates, the branched electron flow of ballistic electrons injected from a quantum point contact is guided by potentials of a tunable height well below the Fermi energy. The transition from injection into an open two-dimensional electron gas to a strongly confined channel exhibits three experimentally distinct regimes: one in which branches spread unrestrictedly, one in which branches are confined but the background conductance is affected very little, and one where the branches have disappeared and the conductance is strongly modified. Classical trajectory-based simulations explain these regimes at the microscopic level. These experiments allow us to understand under which conditions branches observed in scanning gate experiments do or do not reflect the flow of electrons.