Editing Superconductivity (section)

== Classification ==
{{Main|Superconductor classification}}
Superconductors are classified according to many criteria. The most common are:

=== Response to a magnetic field ===
A superconductor can be ''[[Type I superconductor|Type&nbsp;I]]'', meaning it has a single [[critical field]], above which superconductivity is lost and below which the magnetic field is completely expelled from the superconductor; or ''[[Type II superconductor|Type&nbsp;II]]'', meaning it has two critical fields, between which it allows partial penetration of the magnetic field through isolated points<ref>{{Cite web |title=Superconductivity {{!}} CERN |url=https://home.cern/science/engineering/superconductivity |access-date=2020-10-29 |website=home.cern}}</ref> called [[Quantum vortex|vortices]].<ref>{{Cite web |last=Orthacker |first=Angelina |title=Superconductivity |url=http://lampx.tugraz.at/~hadley/ss2/problems/super/s.pdf |website=Technical University of Graz}}</ref> Furthermore, in multicomponent superconductors it is possible to combine the two behaviours. In that case the superconductor is of [[Type-1.5 superconductor|Type-1.5]].<ref>{{Cite web |date=2009-02-17 |title=Type-1.5 superconductor shows its stripes |url=https://physicsworld.com/a/type-1-5-superconductor-shows-its-stripes/ |access-date=2020-10-29 |website=Physics World |language=en-GB}}</ref>

=== Theory of operation ===
A superconductor is ''[[Conventional superconductor|conventional]]'' if it is driven by electron–phonon interaction and explained by the [[BCS theory]] or its extension, the Eliashberg theory. Otherwise, it is ''[[Unconventional superconductor|unconventional]]''.<ref>{{Cite journal |last=Gibney |first=Elizabeth |author-link=Elizabeth Gibney |date=5 March 2018 |title=Surprise graphene discovery could unlock secrets of superconductivity |department=News |journal=Nature |volume=555 |issue=7695 |pages=151&ndash;152 |bibcode=2018Natur.555..151G |doi=10.1038/d41586-018-02773-w |pmid=29517044 |quote=Superconductors come broadly in two types: conventional, in which the activity can be explained by the mainstream theory of superconductivity, and unconventional, where it can't. |doi-access=free}}</ref><ref>{{Cite journal |last1=Hirsch |first1=J. E. |last2=Maple |first2=M. B. |last3=Marsiglio |first3=F. |date=2015-07-15 |title=Superconducting materials classes: Introduction and overview |url=https://www.sciencedirect.com/science/article/pii/S0921453415000933 |journal=Physica C: Superconductivity and Its Applications |series=Superconducting Materials: Conventional, Unconventional and Undetermined |volume=514 |pages=1–8 |arxiv=1504.03318 |bibcode=2015PhyC..514....1H |doi=10.1016/j.physc.2015.03.002 |issn=0921-4534}}</ref> Alternatively, a superconductor is called unconventional if the superconducting [[order parameter]] transforms according to a non-trivial [[irreducible representation]] of the system's [[point group]] or [[space group]].<ref name="c7182">{{cite book |last1=Mineev |first1=V.P. |title=Introduction to Unconventional Superconductivity |last2=Samokhin |first2=K |date=1999-09-21 |publisher=CRC Press |isbn=978-90-5699-209-5 |publication-place=Amsterdam |pages=vii, 20}}</ref>

=== Critical temperature ===
A superconductor is generally considered ''[[High-temperature superconductivity|high-temperature]]'' if it reaches a superconducting state above a temperature of 30&nbsp;K (−243.15&nbsp;°C);<ref>{{Cite journal |last=Grant |first=Paul Michael |date=2011 |title=The great quantum conundrum |journal=Nature |publisher=Nature Publishing Group, a division of Macmillan Publishers Limited. All Rights Reserved. |volume=476 |issue=7358 |pages=37–39 |doi=10.1038/476037a |pmid=21814269 |s2cid=27665903}}</ref> as in the initial discovery by [[Georg Bednorz]] and [[K. Alex Müller]].<ref name="Bednorz2" /> It may also reference materials that transition to superconductivity when cooled using [[liquid nitrogen]] – that is, at only ''T''<sub>c</sub>&nbsp;>&nbsp;77&nbsp;K, although this is generally used only to emphasize that liquid nitrogen coolant is sufficient. Low temperature superconductors refer to materials with a critical temperature below 30&nbsp;K, and are cooled mainly by [[liquid helium]] (''T''<sub>c</sub>&nbsp;>&nbsp;4.2&nbsp;K). One exception to this rule is the [[Iron-based superconductor|iron pnictide]] group of superconductors that display behaviour and properties typical of high-temperature superconductors, yet some of the group have critical temperatures below 30&nbsp;K.

=== Material ===
[[File:Periodic_table_with_superconducting_temperatures.jpg|thumb|Top: Periodic table of superconducting elemental solids and their experimental critical temperature (T){{br}}Bottom: Periodic table of superconducting binary hydrides (0–300&nbsp;GPa). Theoretical predictions indicated in blue and experimental results in red<ref>{{cite journal |author=Flores-Livas |first=José A. |display-authors=et. al. |date=29 April 2020 |title=A perspective on conventional high-temperature superconductors at high pressure: Methods and materials |journal=Physics Reports |volume=856 |pages=1–78 |arxiv=1905.06693 |bibcode=2020PhR...856....1F |doi=10.1016/j.physrep.2020.02.003 |s2cid=155100283}}</ref>]]
Superconductor material classes include [[Chemical element|chemical elements]] (e.g. [[Mercury (element)|mercury]] or [[lead]]), [[Alloy|alloys]] (such as [[niobium–titanium]], [[germanium–niobium]], and [[niobium nitride]]), [[Ceramic|ceramics]] ([[YBCO]] and [[magnesium diboride]]), [[Iron-based superconductor|superconducting pnictides]] (like fluorine-doped LaOFeAs), [[single-layer materials]] such as [[graphene]] and [[Chalcogenide|transition metal dichalcogenides]],<ref>{{Cite web |last=Wood |first=Charlie |date=2024-12-06 |title=Exotic New Superconductors Delight and Confound |url=https://www.quantamagazine.org/exotic-new-superconductors-delight-and-confound-20241206/ |access-date=2025-04-16 |website=Quanta Magazine |language=en}}</ref> or [[Organic superconductor|organic superconductors]] ([[Fullerene|fullerenes]] and [[Carbon nanotube|carbon nanotubes]]; though perhaps these examples should be included among the chemical elements, as they are composed entirely of [[carbon]]).<ref>{{Cite journal |last1=Hirsch |first1=J. E. |last2=Maple |first2=M. B. |last3=Marsiglio |first3=F. |date=2015-07-15 |title=Superconducting materials classes: Introduction and overview |journal=Physica C: Superconductivity and Its Applications |series=Superconducting Materials: Conventional, Unconventional and Undetermined |language=en |volume=514 |pages=1–8 |arxiv=1504.03318 |bibcode=2015PhyC..514....1H |doi=10.1016/j.physc.2015.03.002 |issn=0921-4534 |s2cid=12895850}}</ref><ref>{{Cite web |title=Classification of Superconductors |url=https://cds.cern.ch/record/1252368/files/978-3-540-70977-0_BookBackMatter.pdf |website=CERN}}</ref>