Topological Materials Become Switchable

© Raphael Bühler Because they are extremely stable, so-called "topological states" play an important role in materials research. Now, for the first time, it has been possible to switch such states on and off. A donut is not a breakfast roll. Those are two very clearly distinguishable objects: One has a hole, the other does not. In mathematics, the two shapes are said to be topologically different - you cannot transform one into the other by small, continuous deformations. Therefore, the difference between them is robust to perturbations: Even if you knead and bend the bun it still doesn't look like a donut. Such topological properties also play an important role in material science, albeit in a somewhat more abstract way.