Graphene, a sheet of carbon just one atom thick, can change its magnetic properties the way water changes shape: sometimes flowing, sometimes freezing into ice. In a new study, physicists peered inside this process for the first time using a sensor the size of a needle tip. The sensor detects magnetic fields the way a finger senses the warmth of a radiator — from a distance.

It turns out that the transition between states in graphene is not a smooth glide but a sharp jump. It's as if water doesn't cool gradually but instantly turns to ice at zero. At the same time, flickering magnetic patches appear at the boundary between two states, like ice floes in still-liquid water. This means the two states can coexist, competing for space.

Such jumps matter: if we learn to control them, we could create switches for quantum computers. Graphene's magnetic state is like a light switch: click, and current flows. Only instead of current, it's the electron spin, the particle's internal "top."

The work shows for the first time that topological transitions in graphene are abrupt, like changes in water's aggregate states. This changes our view of the nature of quantum phases and opens the path to new devices.