Editing Unconventional superconductor (section)

==Possible mechanisms==
<!-- huge overlap with High-temperature_superconductivity#Possible_mechanism -->
The most controversial topic in condensed matter physics has been the mechanism for high-''T''<sub>c</sub> superconductivity (HTS). There have been two representative theories on the HTS :  (See also [[Resonating valence bond theory]] )

===Weak-coupling theory===
Firstly, it has been suggested that the HTS emerges by antiferromagnetic spin fluctuation in a doped system.<ref>{{cite journal|author=P. Monthoux|journal=Phys. Rev. B|volume=46|year=1992|title=Weak-coupling theory of high-temperature superconductivity in the antiferromagnetically correlated copper oxides|doi=10.1103/PhysRevB.46.14803|issue=22|bibcode=1992PhRvB..4614803M|last2=Balatsky|first2=A.|last3=Pines|first3=D.|pages=14803–14817|pmid=10003579|display-authors=etal}}</ref> According to this [[weak-coupling theory]], the pairing wave function of the HTS should have a ''d''<sub>''x''<sup>2</sup>−''y''<sup>2</sup></sub> symmetry. Thus, whether the symmetry of the pairing wave function is the ''d'' symmetry or not is essential to demonstrate on the mechanism of the HTS in respect of the spin fluctuation. That is, if the HTS order parameter (pairing wave function) does not have ''d'' symmetry, then a pairing mechanism related to spin fluctuation can be ruled out. The ''tunnel experiment'' (see below) seems to detect ''d'' symmetry in some HTS.

===Interlayer coupling model===
Secondly, there is the [[interlayer coupling model]], according to which a layered structure consisting of BCS-type (s symmetry) superconductor can enhance the superconductivity by itself.<ref>{{cite journal|author=S. Chakravarty|journal=Science|volume=261|pages=337–40|year=1993|title=Interlayer Tunneling and Gap Anisotropy in High-Temperature Superconductors|doi=10.1126/science.261.5119.337|pmid=17836845|issue=5119|bibcode=1993Sci...261..337C|last2=Sudbo|first2=A.|last3=Anderson|first3=P. W.|last4=Strong|first4=S.|s2cid=41404478|display-authors=etal}}</ref> By introducing an additional tunneling interaction between each layer, this model successfully explained the anisotropic symmetry of the order parameter in the HTS as well as the emergence of the HTS.{{citation needed|date=June 2020}}

===Superexchange===
Promising experimental results from various researchers in September 2022, including [[Weijiong Chen]], [[J. C. Séamus Davis|J.C. Séamus Davis]] and [[H. Eisiaki]] revealed that [[superexchange]] of electrons is possibly the most probable reason for high-temperature superconductivity.<ref>{{Cite journal |last1=O’Mahony |first1=Shane M. |last2=Ren |first2=Wangping |last3=Chen |first3=Weijiong |last4=Chong |first4=Yi Xue |last5=Liu |first5=Xiaolong |last6=Eisaki |first6=H. |last7=Uchida |first7=S. |last8=Hamidian |first8=M. H. |last9=Davis |first9=J. C. Séamus |date=2022-09-13 |title=On the electron pairing mechanism of copper-oxide high temperature superconductivity |journal=Proceedings of the National Academy of Sciences |language=en |volume=119 |issue=37 |pages=e2207449119 |doi=10.1073/pnas.2207449119 |issn=0027-8424 |pmc=9477408 |pmid=36067325|arxiv=2108.03655 |bibcode=2022PNAS..11907449O }}</ref><ref>{{Cite magazine |last=Wood |first=Charlie |title=The High-Temperature Superconductivity Mystery Is Finally Solved |language=en-US |magazine=Wired |url=https://www.quantamagazine.org/high-temperature-superconductivity-understood-at-last-20220921/ |access-date=2022-12-26 |issn=1059-1028}}</ref>