A superconductor is a substance that reaches superconductivity, a state of matter in which there is no electrical resistance and magnetic forces cannot penetrate.
A superconductor's electric current can last endlessly.
Superconductivity is often only possible at extremely low temperatures.
Examples of Superconductors:
Niobium,
Magnesium diboride,
Cuprates such as yttrium barium copper oxide, and iron pnictides are all examples of superconductors.