Superconductor allows the construction of SDI Defense buildings, the only city defense against devastating nuclear missiles.
It is a prerequisite of fusion power.
Civilopedia
When electric current is passed through a conductor, such as a copper wire, a small but significant amount of the current is lost to resistance. When certain substances are cooled to temperatures near absolute zero, this resistance disappears. This phenomenon is called superconductivity, and a substance with no electrical resistance is a Superconductor. If such a material could be found that worked at something nearer normal temperatures, its discovery might revolutionize everyday life by greatly reducing the cost of energy and making hosts of new inventions practical.