A flat sheet of material just one atom thick can conduct current only along its edges, like water flowing along the rims of a tray rather than across its middle. In a new study, physicists showed that such edge "channels" can be rearranged simply by rotating an invisible magnetic axis within the sheet.
In a material where electrons behave as massless particles, special points emerge — nodes where a particle's energy does not depend on the direction of motion. One point sits at the center, while several others are scattered around it. Between them, electronic channels run along the sheet's edge. When the magnetic axis is rotated, these side points shift, and the channels rewire, like railway switches routing trains onto new tracks.
If the magnetic axis is instead oriented perpendicular to the sheet, some electronic states disappear, but one central point remains, along with an edge current that flows in only one direction. This is like a one-way road along the perimeter: electrons cannot turn back. Such a current is protected from scattering by defects and thus loses almost no energy.
Rotating the magnetic axis is a simple and precise way to control topological channels. This could be useful for creating switches and logic elements where signals travel along the film's edge without heating or loss.
Edge currents in such materials resemble cars moving through a roundabout: each lane is one-way, and collisions are almost impossible.