A superconductor is a material that, when cooled sufficiently, conducts electricity without losses, like water flowing through a perfectly smooth pipe. But if you hit it with a brief flash of light, it quickly loses this property. In the new experiment, scientists illuminated a thin film of niobium nitride and measured how many billionths of a second it took for superconductivity to disappear.
The decay time turned out not to be constant. When the flash's energy is just enough to destroy the superconducting state, the process suddenly slows down. This is like a ball being pushed toward the top of a hill: if the force is barely sufficient, the ball lingers at the crest before rolling down. Here, the crest is the boundary between the superconducting and normal states.
Slowing down near a critical point is a well-known phenomenon in physics. For example, water near its boiling point takes its time before turning into vapor. But in superconductors, this behavior has now been observed in real time for the first time — previously it was only discussed in calculations. Now scientists have a way to directly monitor how a system passes through a critical point, which will help us better understand the materials of the future.
Niobium nitride is a superconductor used in single-photon detectors: it can detect even a single quantum of light.
In Liu Cixin's novel "The Three-Body Problem," superconducting materials help build devices that operate at the limits of physical laws.