New model can detect ballistic electrons under realistic conditions

Ballistic electrons are among the most fascinating phenomena in modern quantum materials. Unlike ordinary electrons, they do not dissipate imperfections in the material and therefore travel from A to B with virtually no resistance, like a capsule in a pneumatic tube. This behavior often occurs in materials confined to one or two dimensions.

Researchers from Forschungszentrum Jülich and RWTH Aachen University have developed a model that can detect this distinct flow of electrons under realistic conditions. The work was published as an editorial suggestion in the journal Physical Examination Letters.

Ballistic electronic channels that form along the edges of two-dimensional topological materials are considered very promising for future electronics: they could form the basis of energy-efficient circuits and quantum computers with robust qubits.

The new approach builds on the theory of ballistic charge transport developed by Rolf Landauer several decades ago. However, his classical model only describes an idealized case: Landauer assumes that electrons can only enter or leave such a channel at its ends.

The new model from Jülich, however, goes even further. It considers that such a ballistic charge channel does not exist in isolation but forms the edge of an equally conductive material through which the current is injected. Electrons can therefore enter or exit over the entire length of the channel.

“This allows us to describe for the first time the behavior of these peripheral channels in a way that reflects what actually happens in experiments,” explains first author Dr. Kristof Moors.

“Our theory also provides distinct signatures that can be used to identify lossless ballistic current flow and distinguish it from conventional charge transport,” explains Moors, who joined the Imec nanoelectronics research center in Leuven, Belgium, after his postdoctoral fellowship at the Peter Grünberg Institute (PGI-9) in Juliers.

The model shows that the current flow through the two-dimensional material fundamentally changes due to the presence of a ballistic channel. It predicts characteristic voltage distributions that can be directly observed with nanoscale probes or multi-tip scanning tunneling microscopes. This makes it possible to experimentally distinguish between ballistic and dissipative, i.e. lossy, currents, a crucial step to prove beyond doubt the existence of these exotic conduction channels and exploit them for future devices.