At very low temperatures, the electric and magnetic properties of some materials such as lead, mercury and some oxides radically change. These materials become superconductors: they stop showing any electric resistance and expel the magnetic fields. This phenomenon, which was discovered a hundred years ago, is quite an impressive illustration of quantum physics on a human scale: the many free electrons of the material merge into a quantum wave which spreads across very large distances.
Today, superconductivity is an extremely active field of research which includes solving the original mechanism, creating new superconductors, and finding yet new applications. Superconductivity also enables spectacular feats of levitation.
