What Is a Superconductor? (And Why They Matter)

A superconductor is a material that, when cooled below a certain critical temperature, conducts electricity with exactly zero resistance. No energy is lost as heat. A current started in a superconducting loop would, in principle, flow forever.

Two defining behaviours

1. Zero electrical resistance — below its critical temperature, the material lets current pass with no loss. This was discovered in mercury by Heike Kamerlingh Onnes in 1911.
2. The Meissner effect — a superconductor expels magnetic fields from its interior. This is what makes a magnet levitate above a superconductor, and it is the deeper signature that distinguishes a true superconductor from a merely perfect conductor.

Why it happens

In ordinary metals, electrons scatter off vibrating atoms, wasting energy as heat (that is resistance). In a conventional superconductor, electrons pair up (into “Cooper pairs”) and move through the lattice in a coordinated way that avoids scattering entirely. Explaining this earned the 1972 Nobel Prize (BCS theory).

The catch: temperature

Most superconductors only work when extremely cold — often near absolute zero, cooled with liquid helium. High-temperature superconductors (like YBCO) work at higher temperatures but still need cooling with liquid nitrogen. The dream of a room-temperature, ambient-pressure superconductor remains unproven despite recurring claims.

Where superconductors are used

• MRI scanners — superconducting magnets create the strong, stable fields that image the body.
• Maglev trains — magnetic levitation for frictionless high-speed transport.
• Fusion reactors — high-temperature superconducting magnets confine plasma in modern tokamaks.
• Particle accelerators — the magnets that steer beams at facilities like CERN.
• Quantum computers — many quantum computers use superconducting qubits.

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