Superconductors usually don't get along with magnets: a strong field destroys the state in which current flows without resistance. But in thin layers of carbon, things are different.
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.