Superconductors

In conventional superconductors, superconductivity is caused by a force of attraction between certain conduction electrons arising from the exchange of phonons, 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 superconduct 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 aluminium, 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.

Material	Temperature [K]	Temperature [°C]
Zn	0.88	-272.27
Al	1.19	-271.96
Sn	3.72	-269.43
Hg	4.15	-269.00
Pb	7.18	-265.97
Nb	9.46	-263.69
Nb3Sn	18.05	-255.10
Nb3Ge	23.2	-249.95
YBa2Cu3O7	90	-183.15
Bi-Sr-Ca-Cu-O	105	-168.15
Tl-Ba-Ca-Cu-O	125	-148.15