Superconductivity

WikipediA defines:
Superconductivity as a phenomenon occurring in certain materials at extremely low temperatures, characterized by exactly zero electrical resistance.
High-temperature superconductors as a family of material with a common structural feature, relatively well separated copper-oxide planes. They are also called cuprate superconductors. The temperature of superconducting transition that can be achieved in some compounds in this family is highest among all known superconductors.