Editing State of matter (section)

==Superfluids and condensates==

===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>

===Superfluid===
[[Image:Liquid helium Rollin film.jpg|thumb|[[Liquid helium]] in a superfluid phase creeps up on the walls of the cup in a [[Rollin film]], eventually dripping out from the cup.]]
{{Main|Superfluid}}
Close to absolute zero, some liquids form a second liquid state described as '''superfluid''' because it has zero [[viscosity]] (or infinite fluidity; i.e., flowing without friction). This was discovered in 1937 for [[helium]], which forms a superfluid below the [[lambda point|lambda temperature]] of {{convert|2.17|K|C F}}. In this state it will attempt to "climb" out of its container.<ref>
{{cite web
 |author      = J.R. Minkel
 |date        = 20 February 2009
 |title       = Strange but True: Superfluid Helium Can Climb Walls
 |url         = https://www.scientificamerican.com/article.cfm?id=superfluid-can-climb-walls
 |website        = [[Scientific American]]
 |access-date  = 23 February 2010
 |url-status=live
 |archive-url  = https://web.archive.org/web/20110319072600/https://www.scientificamerican.com/article.cfm?id=superfluid-can-climb-walls
 |archive-date = 19 March 2011
 |df          = dmy-all
}}</ref> It also has infinite [[thermal conductivity]] so that no [[temperature gradient]] can form in a superfluid. Placing a superfluid in a spinning container will result in [[quantum vortex|quantized vortices]].

These properties are explained by the theory that the common isotope [[helium-4]] forms a [[Bose–Einstein condensate]] (see next section) in the superfluid state. More recently, [[fermionic condensate]] superfluids have been formed at even lower temperatures by the rare isotope [[helium-3]] and by [[Isotopes of lithium|lithium-6]].<ref>
{{cite web
 |author      = L. Valigra
 |date        = 22 June 2005
 |url         = https://web.mit.edu/newsoffice/2005/matter.html
 |title       = MIT physicists create new form of matter
 |publisher   = [[Massachusetts Institute of Technology|MIT News]]
 |access-date  = 23 February 2010
 |url-status=live
 |archive-url  = https://web.archive.org/web/20131211202945/https://web.mit.edu/newsoffice/2005/matter.html
 |archive-date = 11 December 2013
 |df          = dmy-all
}}</ref>

===Bose–Einstein condensate===
[[Image:Bose Einstein condensate.png|right|thumb|Velocity in a gas of [[rubidium]] as it is cooled: the starting material is on the left, and Bose–Einstein condensate is on the right.]]
{{Main|Bose–Einstein condensate}}
In 1924, [[Albert Einstein]] and [[Satyendra Nath Bose]] predicted the "Bose–Einstein condensate" (BEC), sometimes referred to as the fifth state of matter. In a BEC, matter stops behaving as independent particles, and collapses into a single quantum state that can be described with a single, uniform wavefunction.

In the gas phase, the Bose–Einstein condensate remained an unverified theoretical prediction for many years. However in 1995, the research groups of [[Eric Cornell]] and [[Carl Wieman]], of [[JILA]] at the [[University of Colorado at Boulder]], produced the first such condensate experimentally. A Bose–Einstein condensate is "colder" than a solid. It may occur when atoms have very similar (or the same) [[Energy level|quantum levels]], at temperatures very close to [[absolute zero]], {{convert|−273.15|C|F}}.

===Fermionic condensate===
{{main|Fermionic condensate}}
A ''fermionic condensate'' is similar to the Bose–Einstein condensate but composed of [[fermion]]s. The [[Pauli exclusion principle]] prevents fermions from entering the same quantum state, but a pair of fermions can behave as a boson, and multiple such pairs can then enter the same quantum state without restriction.