What Is a Superconductor?

In 1911, Dutch physicist Heike Kamerlingh Onnes discovered that mercury completely loses electrical resistance at 4.2 K (-269 °C). In a superconductor, electrons form "Cooper pairs" that move through the crystal lattice without scattering, eliminating resistance entirely. This means an electric current can flow forever without losing energy. Superconductors also expel magnetic fields (the Meissner effect), which is why a magnet can levitate above a superconductor. Current applications include MRI machines, particle accelerators, and maglev trains. The holy grail of the field is room-temperature superconductivity, which would revolutionise power transmission and computing.