Some metals conduct electricity with zero resistance

In 1911, Dutch physicist Heike Kamerlingh Onnes cooled a wire of solid mercury in liquid helium and watched its electrical resistance vanish entirely at about 4.2 kelvin (around −269 °C). He called the new state superconductivity.

In an ordinary wire, resistance turns some electricity into wasted heat — roughly 6% of US grid power is lost this way. A superconductor loses none. A current set looping in a superconducting ring can circulate for years with no measurable decay. The reason stayed mysterious for decades until 1957, when Bardeen, Cooper, and Schrieffer worked out the mechanism: at low temperatures electrons pair up into Cooper pairs that glide through the lattice in lockstep, no longer scattering off it. The trio shared a Nobel Prize for the theory that bears their initials.

Zero resistance isn’t the whole story. A superconductor also actively expels magnetic fields — the Meissner effect — which is why a magnet hovers above one rather than merely sitting on a frictionless surface. That expulsion, not resistance alone, is what makes maglev levitation possible.

For 75 years superconductivity demanded brutal cold. Then in 1986, Georg Bednorz and K. Alex Müller found copper-oxide ceramics that superconduct above 77 K, the boiling point of cheap liquid nitrogen — a breakthrough that won the very next year’s Nobel.

Today superconductors power MRI scanners, particle accelerators, and maglev trains, while a room-temperature superconductor at ordinary pressure remains the field’s holy grail.