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 scatter off imperfections in the material and therefore travel from A to B with almost no resistance—like a capsule in a pneumatic tube. This behavior often occurs in confined one- or two-dimensional materials.

Researchers at Forschungszentrum Jülich and RWTH Aachen University have now developed a model that can detect this distinct flow of electrons under realistic conditions. The work was published as an Editors’ Suggestion in the journal Physical Review Letters.

Ballistic electron channels forming along the edges of two-dimensional topological materials are regarded as highly promising for future electronics: they could form the basis for 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 assumed that electrons can enter or leave such a channel only at its ends.

The new Jülich model, however, takes a decisive step further. It considers that such a ballistic charge channel does not exist in isolation but forms the edge of a likewise conductive material through which the current is injected. Electrons can therefore enter or exit along the entire length of the channel.

“This allows us to describe the behavior of such edge channels for the first time in a way that reflects what actually happens in experiments,” says 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,” says Moors, who moved to the Imec nanoelectronics research center in Leuven, Belgium, after his postdoctoral fellowship at the Peter Grünberg Institute (PGI-9) in Jülich.

The model shows that the current flow through the two-dimensional material changes fundamentally 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—that is, lossy—currents, a crucial step towards proving the existence of these exotic conduction channels beyond doubt and harnessing them for future devices.