A crystal is like a city: if the streets are crooked, traffic jams. In a crystal, the streets are atomic rows, and the traffic is the flow of electrons. Any tiny imperfection, impurity, or atomic displacement makes electrons scatter. Scientists from several labs have learned to grow crystals so that the "streets" are almost perfectly straight.

The method is called horizontal vapor transport. The material is slowly transported along the surface, giving atoms time to settle into their proper places. This technique had been used before for some crystals, but for WTe2—a compound of tungsten and tellurium: it was perfected. As a result, disorder dropped tenfold. It's as if only one brick out of a thousand were laid crooked.

What did this achieve? First, when cooled to a few kelvin (minus 270 degrees Celsius), the crystal's resistance changes in a magnetic field more than that of any other metal. Second, if you peel off a layer just one atom thick, you can now see quantum oscillations, periodic resistance fluctuations that reveal the internal structure of electronic states, for the first time. Finally, applying an electric field to this monolayer can drive it into a superconducting state at a temperature of nearly 1.8 K. For such a material, that's a record.

Why does this matter? The cleaner the crystal, the more precisely you can control its properties. WTe2 is a topological semimetal: it has special electronic states that are protected from scattering. Such materials are being considered for future electronics, where information is encoded not by charge but by quantum state. Clean crystals are like new, smooth roads for these technologies.

The horizontal vapor transport method can be applied to other compounds as well. If it works as well as it did for WTe2, we'll get ultra-clean crystals for a host of applications, from quantum computers to magnetic field sensors. And it all started with someone deciding: let atoms stack slowly and carefully, like bricks in a mason's hands, not haphazardly.