Andreas Kreisel

A superconductor is like a city where electric current flows without traffic lights or jams. But the crystal UTe2 has a quirk: its surface follows different rules than its interior. On the tellurium atoms sitting at the surface, electrons found a 'loophole'—states with energies that are forbidden inside the crystal.

Two ultrathin sheets, resembling mica, lie on top of each other. One shifts by a fraction of a nanometer, and a modest semiconductor turns into a magnet. That's roughly how the materials studied by the authors work: layered compounds of niobium and tantalum with sulfur or selenium.