Superconductivity is a phenomenon occurring in certain materials at low temperatures, characterized by the complete absence of electrical resistance and the damping of the interior magnetic field (the Meissner effect.) Superconductivity is a quantum-mechanical phenomenon that is different from perfect conductivity.
In conventional superconductors, superconductivity is caused by a force of attraction between certain conduction electrons arising from the exchange of photons, which causes the conduction electrons to exhibit a superfluid phase composed of correlated pairs of electrons. There also exists a class of materials, known as unconventional superconductors, that exhibit superconductivity but whose physical properties contradict the theory of conventional superconductors. In particular, the so-called high-temperature superconductors super conduct at temperatures much higher than should be possible according to the conventional theory (though still far below room temperature.) There is currently no complete theory of high-temperature superconductivity.
Superconductivity occurs in a wide variety of materials, including simple elements like tin and aluminum, various metallic alloys, some heavily-doped semiconductors, and certain ceramic compounds containing planes of copper and oxygen atoms. The latter class of compounds, known as the cuprates, are high-temperature superconductors. Superconductivity does not occur in noble metals like gold and silver, nor in most ferromagnetic metals, though a number of materials displaying both superconductivity and ferromagnetism have been discovered in recent years.
Source: CDX Global & Wikipedia - en.wikipedia.org
