Fengqi Song

All matter, from stars to humans, is built from particles that in the Standard Model are divided into two families. But there's a third, rare kind — particles that, when swapped, don't just exchange places but tie themselves into a knot, remembering the intertwining rather than the path.

Certain materials, when placed in a strong magnetic field at low temperatures, exhibit a surprising property: their interior stops conducting, becoming an insulator, while along the very edge of the sample electricity runs like a river along a channel, always in one direction.