Superconductivity
Definition
When certain materials cooled near absolute zero conduct electricity with literally zero resistance — currents can circle forever.
Technical definition
Below a critical temperature T_c, electrons form Cooper pairs (BCS theory) and move without scattering; the material also expels magnetic fields (Meissner effect).
Example
MRI magnets are superconducting coils carrying thousands of amps with no heat loss — once charged, the current persists for years.
Common confusion
No verified room-temperature superconductor exists as of 2026. So-called 'high-temperature' superconductors still need −135 °C or colder.