The crystal CeRh₂As₂ behaves like a switch: cool it down and it becomes a superconductor, then bring a magnet close and it abruptly jumps to another superconducting state. Such behavior is rare: most superconductors have only one state, but here there are two, separated by a sharp boundary.

To figure out what's going on, researchers sent ultrasonic waves through the crystal at low temperatures, in strong magnetic fields, and under high pressure. The speed and attenuation of sound change when something inside the material rearranges. It turned out that in both superconducting states, the order is described by a single quantity, as if the switch had one button, not two. This confirms that the cause lies in local symmetry breaking in the crystal: the cerium and rhodium atoms are arranged so that electrons don't have identical conditions in all directions, giving rise to two different superconducting states.

Moreover, analysis of elastic anomalies pointed to the presence of an incommensurate magnetic structure (its period doesn't match that of the crystal lattice), which coexists with superconductivity. It's as if two different orders live inside the crystal without interfering with each other.

Such materials are important not only for understanding fundamental physics but also for future technologies: superconductors with switchable states could become the basis for new types of electronics where information is stored and processed without energy loss.