Cooled near absolute zero, mercury's resistance didn't fade — it vanished completely

In 1911, Heike Kamerlingh Onnes, who had just learned to liquefy helium, cooled solid mercury to about 4.2 kelvin and watched its electrical resistance disappear entirely rather than gradually drop. He had discovered superconductivity, a state where current flows with zero resistance, opening an entirely new field of physics.

— Heike Kamerlingh Onnes, History of superconductivity — Communications from the Physical Laboratory of the University of Leiden, 1911