Normally, current flows equally well in both directions if there's no magnet. A magnetic field or magnetic material breaks that symmetry: electrons start to prefer one direction. But in a new study, physicists found a way to do without magnets.
In a crystal, atoms may not sit perfectly ordered but with some disorder. Electrons scatter off these irregularities, like a ball bouncing left and right on a bumpy path. It turns out that this scattering can make current flow more readily in one direction than the other. The effect strengthens when the number of electrons changes — for example, in bilayer graphene at a certain gate voltage.
This behavior resembles a diode, but without a semiconductor junction. If we learn to control this effect, we could build electronics that don't need bulky magnets. That would simplify circuits and pave the way for miniature devices.
Disorder usually hinders conductivity, but here it actually creates a useful property — current starts to 'favor' one direction.