How Superconductivity Was Discovered

Some materials, when cooled enough, lose all electrical resistance — carrying current forever without losing a drop of energy. This astonishing phenomenon, superconductivity, was discovered in 1911, and like many great findings it emerged not from a search for it but from a quest to reach the coldest temperatures ever achieved.

The race to the cold

In the early twentieth century, a fierce scientific race was underway: who could liquefy the gases that resist becoming liquid, and reach ever closer to absolute zero, the coldest possible temperature? The Dutch physicist Heike Kamerlingh Onnes, working at Leiden, won a crucial victory in 1908 when he became the first to liquefy helium, reaching within a few degrees of absolute zero. This gave him a unique tool: the ability to chill materials colder than anyone else on Earth.

A question about resistance

Onnes turned this new power toward a debated question: what happens to a metal's electrical resistance as it approaches absolute zero? Some thought resistance would gradually fall to zero. Others believed electrons would freeze in place, causing resistance to shoot up to infinity. To find out, Onnes cooled a thread of very pure mercury to the temperature of liquid helium and measured how it conducted electricity.

The shock

What he found astonished him. As the mercury cooled, its resistance dropped as expected — and then, at about four degrees above absolute zero, it did not just become small. It vanished entirely, abruptly, as if a switch had been thrown. The electrical resistance dropped to zero. Current could flow through the mercury with no opposition at all.

A genuinely new state

This was not simply very low resistance — it was the complete and sudden disappearance of resistance below a sharp critical temperature. Onnes coined the term "superconductivity" for it. He received the Nobel Prize in Physics in 1913, primarily for his low-temperature work that made the discovery possible. Yet why it happened remained a deep mystery.

Decades to understand

Explaining superconductivity took nearly half a century. Not until 1957 did three physicists — Bardeen, Cooper and Schrieffer — develop a successful theory. The key idea is that at very low temperatures, electrons can pair up and move through the material in perfect coordination, flowing without the collisions that normally cause resistance. It was one of the great triumphs of quantum theory applied to matter.

From curiosity to technology

Superconductivity is now far more than a laboratory marvel. The powerful magnets in MRI scanners rely on superconducting wires. So do the magnets that steer particles in giant accelerators, and experimental systems for levitating trains and transmitting power without loss. The discovery of materials that superconduct at higher (though still cold) temperatures in the 1980s reignited the field, and the search for a room-temperature superconductor — which would transform technology — remains one of physics' great quests.

Key takeaways

• Superconductivity was discovered in 1911 by Kamerlingh Onnes after he learned to liquefy helium.
• Cooled mercury lost all electrical resistance suddenly, below about four degrees above absolute zero.
• A current in a superconductor can flow essentially forever without loss.
• The phenomenon was explained in 1957 by electron pairing, and now powers MRI scanners and particle accelerators.