Editing State of matter (section)

===Superconductor===
{{main|Superconductivity}}
Superconductors are materials which have zero [[electrical resistivity and conductivity|electrical resistivity]], and therefore perfect conductivity. This is a distinct physical state which exists at low temperature, and the resistivity increases discontinuously to a finite value at a sharply-defined transition temperature for each superconductor.<ref name=MAWhite>{{cite book |last1=White |first1=Mary Anne |authorlink=Mary Anne White |title=Properties of Materials |date=1999 |publisher=Oxford University Press |isbn=0-19-511331-4 |pages=254–258}}</ref>

A superconductor also excludes all magnetic fields from its interior, a phenomenon known as the [[Meissner effect]] or perfect [[diamagnetism]].<ref name=MAWhite/> [[Superconducting magnet]]s are used as electromagnets in [[magnetic resonance imaging]] machines.

The phenomenon of superconductivity was discovered in 1911, and for 75 years was only known in some metals and metallic alloys at temperatures below 30 K. In 1986 so-called [[high-temperature superconductivity]] was discovered in certain [[ceramic]] oxides, and has now been observed in temperatures as high as 164 K.<ref name=Tinkham>{{cite book |author=M. Tinkham |year=2004 |title=Introduction to Superconductivity |url=https://books.google.com/books?id=k6AO9nRYbioC&pg=PA17 |publisher=[[Courier Dover Publications|Courier Dover]] |pages=17–23 |isbn=0486435032}}</ref>