What is a superconductor?
A superconductor has no electrical resistance and no interior magnetic field in a superconductor (the Meissner effect), which is usually a characteristic if certain materials at low temperatures. When a current flows through wires it loses energy. In a superconductor, the current does not lose any voltage. So currents can flow around loops without stopping. Once current starts flowing around a loop of superconductor, the electrical current and its magnetism keeps going forever.
Superconductors can be quite a few different materials: tin, aluminium, various metallic alloys, and a few other less common materials.