An ordinary screw only goes into wood if you turn it the right way. A similar rule applies in a crystal of MnTe2 — a close relative of “fool’s gold.” It’s here that physicists discovered magnetic waves can be twisted left or right, and their movement depends on the direction of rotation.

By scanning the crystal with a laser (spectroscopy) and measuring the twist of reflected light (polarimetry), scientists confirmed with computer simulations that magnon waves split into two types. The effect arises from a superposition of vibrational states. In the future, such “unidirectional” waves will be useful for quantum computing: they can transmit signals without interference. At low temperatures, where quantum laws of heat come into play, magnons behave even more strangely, and with quantum optics they can be controlled with high precision. The groundwork for this research was laid by Werner Heisenberg and Lev Landau.