Some materials are internally like a Möbius strip: their electronic states are twisted in a special way. Such topological properties are usually manipulated with a powerful magnetic field, as if trying to flatten the strip with a sledgehammer. A group of researchers has found a more delicate tool.

It turns out that in magnetic topological insulators, a slight rotation of the internal magnetization can do the trick. It's like a key in a lock that opens the door without brute force. In a two-dimensional crystal with a kagome lattice (a pattern of triangles), rotating the magnetization by just 60 degrees makes the topological charge, the Chern number, change sign. Along the way, the material passes through an ordinary, non-topological state.

Simulations confirmed that the switching occurs in exceptionally weak magnetic fields and within picoseconds. Such a "magnetic key" promises ultrafast and energy-efficient memory or logic devices, where information is encoded not by charge but by topology.