Dong Qian

A single-atom-thick sheet of tungsten telluride is like thin foil: electrons can't pass through because there's a band gap between their possible states, like a moat you can't jump across. Add two more layers, and the moat disappears; the material becomes a metal, and current flows. Add more layers, and the properties change again, as if someone is flipping modes with a single button.

In a ballroom where couples were dancing, the music changed, and the pairs lined up in rows suddenly spun into whirlpools. That is how the magnetic crystal Fe3Ge rearranges its internal pattern once the temperature climbs above 375 kelvins, which is about a hundred degrees of heat.