A crystal that looks like a stack of pancakes was placed on a smooth substrate of magnesium oxide. The result was a film only a few hundred atoms thick. When they ran a current through it and switched on a magnet, the resistance jumped by nearly a quarter—22.5% in a 9-tesla field.

Inside the film, electricity is carried by two streams of particles. One stream is fast and light, like motorcyclists on an open highway. The other is slow and heavy, like trucks stuck in traffic. The magnetic field bends their paths differently, so the resistance changes more than it would if there were only one stream.

When the magnet was tilted, the resistance didn't behave uniformly. Along one direction it changed more, along another less. But at certain angles, sharp dips and spikes appeared. These features repeated at all fields and temperatures, like fingerprints that don't depend on how hard you press.

This behavior resembles light playing on layered mica: the layers reflect differently, and the pattern depends on the tilt. In our case, the crystal layers set a direction along which electrons find it easier to run. And the two streams of particles create a complex resistance pattern that we managed to describe with a simple two-carrier model.