View source for Physics:Iron-based superconductor

[[File:LnFePnOFstructure.png|thumb|right|250px|Crystal structure of LnFeAsOF, a 1111-type ferropnictide compound. Ln = [[Chemistry:Lanthanide|lanthanide]] (La, Ce, etc.), Pn = pnictide (As, P, etc.)<ref name=rev1>{{Cite journal | doi = 10.1088/1468-6996/16/3/033503| pmid = 27877784| title = Exploration of new superconductors and functional materials, and fabrication of superconducting tapes and wires of iron pnictides| journal = Science and Technology of Advanced Materials| volume = 16| issue = 3| page = 033503| year = 2015| last1 = Hosono | first1 = H. | last2 = Tanabe | first2 = K. | last3 = Takayama-Muromachi | first3 = E. | last4 = Kageyama | first4 = H. | last5 = Yamanaka | first5 = S. | last6 = Kumakura | first6 = H. | last7 = Nohara | first7 = M. | last8 = Hiramatsu | first8 = H. | last9 = Fujitsu | first9 = S. |pmc=5099821|bibcode = 2015STAdM..16c3503H |arxiv = 1505.02240}}</ref>]]
'''Iron-based superconductors''' ('''FeSC''') are [[Chemistry:Iron|iron]]-containing chemical compounds whose [[Physics:Superconductors|superconducting]] properties were discovered in 2006.<ref name=Hoso2006>{{cite journal|title = Iron-Based Layered Superconductor: LaOFeP |author1=Kamihara, Yoichi |author2=Hiramatsu, Hidenori |author3=Hirano, Masahiro |author4=Kawamura, Ryuto |author5=Yanagi, Hiroshi |author6=Kamiya, Toshio |author7=Hosono, Hideo |journal = J. Am. Chem. Soc.|volume = 128|issue = 31|pages = 10012–10013|year = 2006|doi = 10.1021/ja063355c|pmid = 16881620}}</ref><ref name=hosono26K>{{cite journal|author1=Kamihara, Yoichi |author2=Watanabe, Takumi |author3=Hirano, Masahiro |author4=Hosono, Hideo |journal=Journal of the American Chemical Society|volume=130|pages=3296–3297|year=2008|doi=10.1021/ja800073m|pmid=18293989|title = Iron-Based Layered Superconductor La[O<sub>1–x</sub>F<sub>x</sub>]FeAs (x = 0.05–0.12) with T<sub>c</sub> = 26 K|issue=11}}</ref>
In 2008, led by recently discovered iron pnictide compounds (originally known as [[Physics:Oxypnictide|oxypnictide]]s), they were in the first stages of experimentation and implementation.<ref>{{cite journal|author1=Ozawa, T C   |author2=Kauzlarich, S M |title=Chemistry of layered d-metal pnictide oxides and their potential as candidates for new superconductors|journal=Sci. Technol. Adv. Mater.|volume=9|page=033003|year=2008|doi=10.1088/1468-6996/9/3/033003|bibcode = 2008STAdM...9c3003O|issue=3 |arxiv = 0808.1158 |pmid=27877997 |pmc=5099654}} {{Open access}}</ref> (Previously most [[Physics:High-temperature superconductor|high-temperature superconductor]]s were [[Physics:Cuprate superconductor|cuprate]]s and being based on layers of [[Chemistry:Copper|copper]] and [[Chemistry:Oxygen|oxygen]] sandwiched between other substances (La, Ba, Hg)).

This new type of superconductors is based instead on conducting layers of [[Chemistry:Iron|iron]] and a pnictide ([[Chemistry:Chemical element|chemical element]]s in [[Chemistry:Group (periodic table)|group 15]] of the [[Chemistry:Periodic table|periodic table]], here typically [[Chemistry:Arsenic|arsenic]] (As) and [[Chemistry:Phosphorus|phosphorus]] (P)) and seems to show promise as the next generation of high temperature superconductors.<ref name=SA>[http://www.sciam.com/article.cfm?id=iron-exposed-as-high-temp-superconductor "Iron Exposed as High-Temperature Superconductor"]. Scientific American. June 2008</ref>

Much of the interest is because the new compounds are very different from the cuprates and may help lead to a theory of non-BCS-theory superconductivity.

More recently these have been called the '''ferropnictides'''. The first ones found belong to the group of [[Physics:Oxypnictide|oxypnictide]]s. Some of the compounds have been known since 1995,<ref name=Jei1995>{{cite journal |title = The rate earth transition metal phosphide oxides LnFePO, LnRuPO and LnCoPO with ZrCuSiAs type structure |author1=Zimmer, Barbara I. |author2=Jeitschko, Wolfgang |author3=Albering, Jörg H. |author4=Glaum, Robert |author5=Reehuis, Manfred |journal = Journal of Alloys and Compounds|volume = 229|issue = 2|pages = 238–242|year = 1995|doi = 10.1016/0925-8388(95)01672-4}}</ref> 
and their semiconductive properties have been known and patented since 2006.<ref>Hosono, H. ''et al.'' (2006) [http://www.freepatentsonline.com/EP1868215.html Magnetic semiconductor material] European Patent Application EP1868215</ref>

It has also been found that some iron [[Chemistry:Chalcogen|chalcogen]]s superconduct.<ref>{{cite journal|doi=10.1103/Physics.1.28|title=The iron age of superconductivity|year=2008|last1=Johannes|first1=Michelle|journal=Physics|volume=1|page=28|bibcode = 2008PhyOJ...1...28J |url=https://physics.aps.org/featured-article-pdf/10.1103/PhysRevB.78.134514|doi-access=free}}</ref> The undoped ''β''-FeSe is the simplest iron-based superconductor but with the diverse properties.<ref name="Pustovit2016">{{Cite journal|author1=Yu. V. Pustovit |author2=A. A. Kordyuk |year=2016 |title=Metamorphoses of electronic structure of FeSe-based superconductors (Review article) |journal=Low Temp. Phys. |volume=42 |issue=11 |arxiv=1608.07751|bibcode=2016LTP....42..995P |doi=10.1063/1.4969896 |pages=995–1007 |s2cid=119184569 }}</ref> It has a [[Physics:Superconductivity#Superconducting phase transition|critical temperature (''T''<sub>c</sub>)]] of 8 [[Kelvin|K]] at normal pressure, and 36.7 K under high pressure<ref>{{cite journal|doi=10.1038/nmat2491|pmid=19525948|title=Electronic and Magnetic Phase Diagram of ''β''-Fe<sub>1.01</sub>Se with superconductivity at 36.7 K under pressure|year=2009|last1=Medvedev|first1=S.|last2=McQueen|first2=T. M.|last3=Troyan|first3=I. A.|last4=Palasyuk|first4=T.|last5=Eremets|author5-link=Mikhail Eremets|first5=M. I.|last6=Cava|first6=R. J.|last7=Naghavi|first7=S.|last8=Casper|first8=F.|last9=Ksenofontov|first9=V.|last10=Wortmann|first10=G.|last11=Felser|first11=C.|journal=Nature Materials|volume=8|issue=8|pages=630–633|arxiv = 0903.2143 |bibcode = 2009NatMa...8..630M |s2cid=117714394 }}</ref> and by means of intercalation. The combination of both intercalation and higher pressure results in re-emerging superconductivity at ''T''<sub>c</sub> of up to 48 K (see,<ref name="Pustovit2016"/><ref name="Sun2012">{{Cite journal|author1=Sun, Liling |author2=Chen, Xiao-Jia |author3= Guo, Jing |author4= Gao, Peiwen |author5= Huang, Qing-Zhen |author6= Wang, Hangdong |author7= Fang, Minghu |author8= Chen, Xiaolong |author9= Chen, Genfu |author10= Wu, Qi |author11= Zhang, Chao |author12= Gu, Dachun |author13= Dong, Xiaoli |author14= Wang, Lin |author15= Yang, Ke |author16= Li, Aiguo |author17= Dai, Xi |author18= Mao, Ho-kwang |author19=Zhao, Zhongxian |year=2012 |title= Re-emerging superconductivity at 48 kelvin in iron chalcogenides |journal= Nature |volume= 483 | number = 7387|pages = 67–69|doi= 10.1038/nature10813 |arxiv= 1110.2600 }}</ref> and references therein).

A subset of iron-based superconductors with properties similar to the oxypnictides, known as the [[Physics:122 iron arsenide|122 iron arsenide]]s, attracted attention in 2008 due to their relative ease of synthesis.

The [[Physics:Oxypnictide|oxypnictide]]s such as LaOFeAs are often referred to as the '1111' pnictides.
{{blockquote|The crystalline material, known chemically as LaOFeAs, stacks iron and arsenic layers, where the electrons flow, between planes of [[Chemistry:Lanthanum|lanthanum]] and [[Chemistry:Oxygen|oxygen]]. Replacing up to 11 percent of the oxygen with [[Chemistry:Fluorine|fluorine]] improved the compound — it became superconductive at 26 [[Kelvin|kelvin]], the team reports in the March 19, 2008 Journal of the American Chemical Society. Subsequent research from other groups suggests that replacing the lanthanum in LaOFeAs with other rare earth elements such as [[Chemistry:Cerium|cerium]], [[Chemistry:Samarium|samarium]], [[Chemistry:Neodymium|neodymium]] and [[Chemistry:Praseodymium|praseodymium]] leads to superconductors that work at 52 kelvin.<ref name=SA />}}

<div style="float:right;margin-left:0.5em;">
{|class="wikitable sortable" 
![[Physics:Oxypnictide|Oxypnictide]]
!''T''<sub>c</sub> (K)
|-
|LaO<sub>0.89</sub>F<sub>0.11</sub>FeAs
| 26<ref name=r1>{{cite journal|last1=Ishida|first1=Kenji|last2=Nakai|first2=Yusuke|last3=Hosono|first3=Hideo|title=To What Extent Iron-Pnictide New Superconductors Have Been Clarified: A Progress Report|journal=Journal of the Physical Society of Japan|volume=78|issue=6|year=2009|page=062001|doi=10.1143/JPSJ.78.062001|arxiv = 0906.2045 |bibcode=2009JPSJ...78f2001I|s2cid=119295430}}</ref>
|-
|LaO<sub>0.9</sub>F<sub>0.2</sub>FeAs
| 28.5<ref>{{cite journal|doi = 10.1209/0295-5075/84/57003|title = Potassium fluoride doped LaOFeAs multi-band superconductor: Evidence of extremely high upper critical field|year = 2008|author = Prakash, J.|journal = EPL|volume = 84|page = 57003|first2 = S. J.|first3 = S. L.|first4 = S.|first5 = A. K.|last2 = Singh|last3 = Samal|last4 = Patnaik|last5 = Ganguli|bibcode = 2008EL.....8457003P|issue = 5 |s2cid = 119254951}}</ref>
|-
| CeFeAsO<sub>0.84</sub>F<sub>0.16</sub> 
| 41<ref name=r1/>
|-
| SmFeAsO<sub>0.9</sub>F<sub>0.1</sub> 
| 43<ref name=r1/><ref name=chen2008>{{cite journal|doi = 10.1038/nature07045|pmid = 18500328|title = Superconductivity at 43 K in SmFeAsO<sub>1–x</sub>F<sub>x</sub>|year = 2008|author1=Chen, X. H. |author2=Wu, T. |author3=Wu, G. |author4=Liu, R. H. |author5=Chen, H. |author6=Fang, D. F. |journal = Nature|volume = 453|issue = 7196|pages = 761–762|bibcode = 2008Natur.453..761C|arxiv=0803.3603|s2cid = 115842939}}</ref>
|-
| La<sub>0.5</sub>Y<sub>0.5</sub>FeAsO<sub>0.6</sub>
| 43.1<ref>{{cite journal|bibcode = 2008PhRvB..78q2503S|doi = 10.1103/PhysRevB.78.172503|title = Superconductivity at 43 K at ambient pressure in the iron-based layered compound La1‑xYxFeAsOy|year = 2008|author = Shirage, Parasharam M.|journal = Physical Review B|volume = 78|page = 172503|first2 = Kiichi|first3 = Hijiri|first4 = Hiroshi|first5 = Akira|last2 = Miyazawa|last3 = Kito|last4 = Eisaki|last5 = Iyo|issue = 17}}</ref>
|-
| NdFeAsO<sub>0.89</sub>F<sub>0.11</sub> 
| 52<ref name=r1/>
|-
| PrFeAsO<sub>0.89</sub>F<sub>0.11</sub>
| 52<ref>{{cite journal|doi = 10.1179/143307508X333686|title = Superconductivity at 52 K in iron based F doped layered quaternary compound Pr[O<sub>1–x</sub>F<sub>x</sub>]FeAs|year = 2008|author = Ren, Z. A.|journal = Materials Research Innovations|volume = 12|pages = 105–106|first2 = J.|first3 = W.|first4 = W.|first5 = G. C.|first6 = X. L.|first7 = L. L.|first8 = Z. X.|last2 = Yang|last3 = Lu|last4 = Yi|last5 = Che|last6 = Dong|last7 = Sun|last8 = Zhao|issue = 3|arxiv = 0803.4283| bibcode=2008MatRI..12..105R |s2cid = 55488705}}</ref>
|-
| ErFeAsO<sub>1–y</sub> 
| 45<ref>{{cite journal | doi=10.1209/0295-5075/92/57011 | title=Synthesis of ErFeAsO-based superconductors by the hydrogen doping method | year=2010 | last1=Shirage | first1=Parasharam M. | last2=Miyazawa | first2=Kiichi | last3=Kihou | first3=Kunihiro | last4=Lee | first4=Chul-Ho | last5=Kito | first5=Hijiri | last6=Tokiwa | first6=Kazuyasu | last7=Tanaka | first7=Yasumoto | last8=Eisaki | first8=Hiroshi | last9=Iyo | first9=Akira <!--exactly 9 authors--> | journal=EPL | volume=92 | issue=5 | page=57011 | arxiv = 1011.5022 | bibcode = 2010EL.....9257011S| s2cid=118303767 }}</ref>
|-
| Al-32522 (CaAlOFeAs)
| 30(As), 16.6 (P)<ref name=shirage2>{{cite journal|doi=10.1021/ja110729m|title=Emergence of Superconductivity in "32522" Structure of (Ca<sub>3</sub>Al<sub>2</sub>O<sub>5–y</sub>)(Fe<sub>2</sub>Pn<sub>2</sub>) (Pn = As and P)|year=2011|last1=Shirage|first1=Parasharam M.|last2=Kihou|first2=Kunihiro|last3=Lee|first3=Chul-Ho|last4=Kito|first4=Hijiri|last5=Eisaki|first5=Hiroshi|last6=Iyo|first6=Akira|journal=Journal of the American Chemical Society|volume=133|issue=25|pages=9630–3|pmid=21627302}}</ref>
|-
| Al-42622 (CaAlOFeAs)
| 28.3(As), 17.2 (P)<ref name=shirage1>{{cite journal|doi=10.1063/1.3508957|title=Superconductivity at 28.3 and 17.1 K in (Ca<sub>4</sub>Al<sub>2</sub>O<sub>6−y</sub>)(Fe<sub>2</sub>Pn<sub>2</sub>) (Pn=As and P)|year=2010|last1=Shirage|first1=Parasharam M.|last2=Kihou|first2=Kunihiro|last3=Lee|first3=Chul-Ho|last4=Kito|first4=Hijiri|last5=Eisaki|first5=Hiroshi|last6=Iyo|first6=Akira|journal=Applied Physics Letters|volume=97|issue=17|page=172506|arxiv = 1008.2586 |bibcode = 2010ApPhL..97q2506S |s2cid = 117899145}}</ref>
|-
| GdFeAsO<sub>0.85</sub>
| 53.5<ref>{{cite journal|doi = 10.1088/0953-2048/21/8/082001|title = Superconductivity at 53.5 K in GdFeAsO<sub>1−δ</sub>|year = 2008|author = Yang, Jie|journal = Superconductor Science and Technology|volume = 21|page = 082001|first2 = Zheng-Cai|first3 = Wei|first4 = Wei|first5 = Xiao-Li|first6 = Zhi-An|first7 = Guang-Can|first8 = Xiao-Li|first9 = Li-Ling|last10 = Zhou|first10 = Fang|last11 = Zhao|first11 = Zhong-Xian|last2 = Li|last3 = Lu|last4 = Yi|last5 = Shen|last6 = Ren|last7 = Che|last8 = Dong|last9 = Sun|bibcode = 2008SuScT..21h2001Y|issue = 8|arxiv = 0804.3727| s2cid=121990600 }}</ref>
|-
| BaFe<sub>1.8</sub>Co<sub>0.2</sub>As<sub>2</sub>
| 25.3<ref name=Yin>{{cite journal|doi=10.1103/PhysRevLett.102.097002|arxiv=0810.1048|title=Scanning Tunneling Spectroscopy and Vortex Imaging in the Iron Pnictide Superconductor BaFe<sub>1.8</sub>Co<sub>0.2</sub>As<sub>2</sub>|year=2009|last1=Yin|first1=Yi|last2=Zech|first2=M.|last3=Williams|first3=T. L.|last4=Wang|first4=X. F.|last5=Wu|first5=G.|last6=Chen|first6=X. H.|last7=Hoffman|first7=J. E.|journal=Physical Review Letters|volume=102|issue=9|page=97002|pmid=19392555|bibcode = 2009PhRvL.102i7002Y |s2cid=16583932}}</ref>
|-
|SmFeAsO<sub>~0.85</sub>
| 55<ref name=ren2008>{{cite journal|doi = 10.1209/0295-5075/83/17002|title = Superconductivity and phase diagram in iron-based arsenic-oxides ReFeAsO<sub>1−δ</sub> (Re = rare-earth metal) without fluorine doping|year = 2008|author = Ren, Zhi-An|journal = EPL|volume = 83|page = 17002|first2 = Guang-Can|first3 = Xiao-Li|first4 = Jie|first5 = Wei|first6 = Wei|first7 = Xiao-Li|first8 = Zheng-Cai|first9 = Li-Ling|last10 = Zhou|first10 = Fang|last11 = Zhao|first11 = Zhong-Xian|last2 = Che|last3 = Dong|last4 = Yang|last5 = Lu|last6 = Yi|last7 = Shen|last8 = Li|last9 = Sun| issue=1 |bibcode=2008EL.....8317002R|arxiv = 0804.2582 |s2cid = 96240327}}</ref>
|}

{|class="wikitable" 
!Non-oxypnictide
!''T''<sub>c</sub> (K)
|-
| Ba<sub>0.6</sub>K<sub>0.4</sub>Fe<sub>2</sub>As<sub>2</sub> 
| 38<ref name=Rotter2008>{{cite journal|title = Superconductivity at 38 K in the Iron Arsenide (Ba<sub>1–x</sub>K<sub>x</sub>)Fe<sub>2</sub>As<sub>2</sub>|author1=Rotter, Marianne |author2=Tegel, Marcus |author3=Johrendt, Dirk |journal = Physical Review Letters |volume = 101 |page = 107006|year = 2008|doi = 10.1103/PhysRevLett.101.107006|pmid = 18851249|issue = 10|bibcode=2008PhRvL.101j7006R|arxiv = 0805.4630 |s2cid=25876149 }}</ref> 
|-
| Ca<sub>0.6</sub>Na<sub>0.4</sub>Fe<sub>2</sub>As<sub>2</sub> 
| 26<ref name=shirage>{{cite journal|doi=10.1143/APEX.1.081702|title=Superconductivity at 26 K in (Ca<sub>1–x</sub>Na<sub>x</sub>)Fe<sub>2</sub>As<sub>2</sub>|year=2008|last1=Shirage|first1=Parasharam Maruti|first2=Kiichi|first3=Hijiri|first4=Hiroshi|first5=Akira|journal=Applied Physics Express|volume=1|page=081702|last2=Miyazawa|last3=Kito|last4=Eisaki|last5=Iyo|issue=8 |bibcode=2008APExp...1h1702M|s2cid=94498268 }}</ref>
|-
| CaFe<sub>0.9</sub>Co<sub>0.1</sub>AsF 
| 22<ref name = Mats2008>{{cite journal|title = Superconductivity Induced by Co-Doping in Quaternary Fluoroarsenide CaFeAsF|author1=Satoru Matsuishi |author2=Yasunori Inoue |author3=Takatoshi Nomura |author4=Hiroshi Yanagi |author5=Masahiro Hirano |author6=Hideo Hosono |journal = J. Am. Chem. Soc.|volume = 130|pages = 14428–14429|year = 2008|doi = 10.1021/ja806357j|pmid = 18842039|issue = 44}}</ref> 
|-
| Sr<sub>0.5</sub>Sm<sub>0.5</sub>FeAsF
| 56<ref name=Wu2008>{{cite journal|last1=Wu|first1=G|last2=Xie|first2=Y L|last3=Chen|first3=H|last4=Zhong|first4=M|last5=Liu|first5=R H|last6=Shi|first6=B C|last7=Li|first7=Q J|last8=Wang|first8=X F|last9=Wu|first9=T|last10=Yan|first10=Y J|last11=Ying|first11=J J|last12=Chen|first12=X H|title=Superconductivity at 56 K in samarium-doped SrFeAsF|journal=Journal of Physics: Condensed Matter|volume=21|issue=14|year=2009|page=142203|doi=10.1088/0953-8984/21/14/142203|arxiv=0811.0761|bibcode=2009JPCM...21n2203W|pmid=21825317|s2cid=41728130}}</ref>
|-
| LiFeAs 
| 18<ref name=wang2008>{{cite journal|last1=Wang|first1=X.C.|last2=Liu|first2=Q.Q.|last3=Lv|first3=Y.X.|last4=Gao|first4=W.B.|last5=Yang|first5=L.X.|last6=Yu|first6=R.C.|last7=Li|first7=F.Y.|last8=Jin|first8=C.Q.|title=The superconductivity at 18 K in LiFeAs system|journal=Solid State Communications|volume=148|issue=11–12|year=2008|pages=538–540|arxiv = 0806.4688|doi=10.1016/j.ssc.2008.09.057|bibcode=2008SSCom.148..538W|s2cid=55247836}}</ref><ref name=Pitcher2008>{{cite journal|last1=Pitcher|first1=Michael J.|last2=Parker|first2=Dinah R.|last3=Adamson|first3=Paul|last4=Herkelrath|first4=Sebastian J. C.|last5=Boothroyd|first5=Andrew T.|last6=Ibberson|first6=Richard M.|last7=Brunelli|first7=Michela|last8=Clarke|first8=Simon J.|title=Structure and superconductivity of LiFeAs|journal=Chemical Communications|issue=45|year=2008|pages=5918–20|pmid = 19030538|doi=10.1039/b813153h|arxiv=0807.2228|s2cid=3258249}}</ref><ref name=Tapp2008>{{cite journal|last1=Tapp|first1=Joshua H.|last2=Tang|first2=Zhongjia|last3=Lv|first3=Bing|last4=Sasmal|first4=Kalyan|last5=Lorenz|first5=Bernd|last6=Chu|first6=Paul C. W.|last7=Guloy|first7=Arnold M.|title=LiFeAs: An intrinsic FeAs-based superconductor with ''T''<sub>c</sub>=18&nbsp;K|journal=Physical Review B|volume=78|issue=6|year=2008|page=060505|arxiv = 0807.2274|doi=10.1103/PhysRevB.78.060505|bibcode=2008PhRvB..78f0505T|s2cid=118379012}}</ref>
|-
| NaFeAs 
| 9–25<ref name="Chu2009">{{cite journal|last1=Chu|first1=C.W.|last2=Chen|first2=F.|last3=Gooch|first3=M.|last4=Guloy|first4=A.M.|last5=Lorenz|first5=B.|last6=Lv|first6=B.|last7=Sasmal|first7=K.|last8=Tang|first8=Z.J.|last9=Tapp|first9=J.H.|last10=Xue|first10=Y.Y.|title=The synthesis and characterization of LiFeAs and NaFeAs|journal=Physica C: Superconductivity|volume=469|issue=9–12|year=2009|pages=326–331|arxiv = 0902.0806|doi=10.1016/j.physc.2009.03.016|bibcode=2009PhyC..469..326C|s2cid=118531206}}</ref><ref name="Parker2008">{{cite journal|title = Structure and superconductivity of the layered iron arsenide NaFeAs|author1=Parker, Dinah R. |author2=Pitcher, Michael J. |author3=Clarke, Simon J. |year = 2008|doi = 10.1039/B818911K|journal = Chemical Communications|issue = 16|pages = 2189–91|volume = 2189|arxiv = 0810.3214 |pmid=19360189|s2cid=45189652 }}</ref> 
|-
| [[Chemistry:Iron(II) selenide|FeSe]] 
| <27<ref name="Hsu2008">{{cite journal|title = Superconductivity in the PbO-type structure α-FeSe|author = Fong-Chi Hsu|journal = PNAS|volume = 105|pages = 14262–14264|year = 2008|doi = 10.1073/pnas.0807325105|pmid = 18776050|issue = 38|pmc = 2531064|bibcode=2008PNAS..10514262H|name-list-style=vanc|display-authors = 1|last2 = Luo|first2 = J.-Y.|last3 = Yeh|first3 = K.-W.|last4 = Chen|first4 = T.-K.|last5 = Huang|first5 = T.-W.|last6 = Wu|first6 = P. M.|last7 = Lee|first7 = Y.-C.|last8 = Huang|first8 = Y.-L.|last9 = Chu|first9 = Y.-Y.|last10 = Yan|first10 = Der-Chung|last11 = Wu|first11 = Maw-Kuen|doi-access = free}}</ref><ref name="Mizu2008">{{cite journal|title = Superconductivity at 27&nbsp;K in tetragonal FeSe under high pressure|author1=Mizuguchi, Yoshikazu |author2=Tomioka, Fumiaki |author3=Tsuda, Shunsuke |author4=Yamaguchi, Takahide |author5=Takano, Yoshihiko |journal = Appl. Phys. Lett.|volume = 93|page = 152505|year = 2008|doi = 10.1063/1.3000616|bibcode = 2008ApPhL..93o2505M|issue = 15 |arxiv = 0807.4315 |s2cid=119218961 }}</ref> 
|-
|LaFeSiH
|10<ref name=Bernardini2009>{{cite journal|last1=Bernardini|first1=F.|first2=G. |last2=Garbarino |first3=A. |last3=Sulpice |first4=M. |last4=Núñez-Regueiro |first5=E. |last5=Gaudin |first6=B. |last6=Chevalier |first7=M.-A. |last7=Méasson |first8=A. |last8=Cano |first9=S. |last9=Tencé|title=Iron-based superconductivity extended to the novel silicide LaFeSiH |journal=Physical Review B|volume=97|issue=10|date=March 2018|page=100504|arxiv = 1701.05010|doi=10.1103/PhysRevB.97.100504|bibcode=2018PhRvB..97j0504B |s2cid=119004395|issn=2469-9969}}</ref>
|}
</div>

Iron pnictide superconductors crystallize into the [FeAs] layered structure alternating with spacer or charge reservoir block.<ref name=r1 /> 
The compounds can thus be classified into "1111" system RFeAsO (R: the rare earth element) including LaFeAsO,<ref name=hosono26K/> SmFeAsO,<ref name=chen2008/> PrFeAsO,<ref name=ren2008/> etc.; "122" type BaFe<sub>2</sub>As<sub>2</sub>,<ref name=Rotter2008/> SrFe<sub>2</sub>As<sub>2</sub><ref name=chu2008>{{cite journal|title = Superconducting Fe-Based Compounds (A<sub>1–x</sub>Sr<sub>x</sub>) Fe<sub>2</sub>As<sub>2</sub> with A=K and Cs with Transition Temperatures up to 37 K |journal = Physical Review Letters |volume = 101 |issue = 10|page = 107007|year = 2008 |pmid = 18851250 |doi=10.1103/physrevlett.101.107007|last1 = Sasmal|first1= K.|bibcode = 2008PhRvL.101j7007S|last2= Lv|first2= Bing|last3 = Lorenz|first3 = Bernd|last4 = Guloy|first4 = Arnold M.|last5 = Chen|first5 = Feng|last6 = Xue|first6 = Yu-Yi|last7 = Chu|first7 = Ching-Wu|url = http://repository.ust.hk/ir/bitstream/1783.1-18311/1/PhysRevLett.101.107007.pdf|arxiv = 0806.1301}}</ref> or CaFe<sub>2</sub>As<sub>2</sub>;<ref name=shirage/> "111" type LiFeAs,<ref name=wang2008/><ref name=Pitcher2008/><ref name=Tapp2008/> NaFeAs,<ref name=Chu2009/><ref name=Parker2008/><ref>{{cite journal|last1=Zhang|first1=S. J.|last2=Wang|first2=X. C.|last3=Liu|first3=Q. Q.|last4=Lv|first4=Y. X.|last5=Yu|first5=X. H.|last6=Lin|first6=Z. J.|last7=Zhao|first7=Y. S.|last8=Wang|first8=L.|last9=Ding|first9=Y.|last10=Mao|first10=H. K.|last11=Jin|first11=C. Q.|title=Superconductivity at 31 K in the "111"-type iron arsenide superconductor Na<sub>1−x</sub>FeAs induced by pressure|journal=EPL|volume=88|issue=4|year=2009|page=47008|doi=10.1209/0295-5075/88/47008|bibcode=2009EL.....8847008Z|arxiv=0912.2025|s2cid=55588819}}</ref> and LiFeP.<ref name=Deng2009>{{cite journal|last1=Deng|first1=Z.|last2=Wang|first2=X. C.|last3=Liu|first3=Q. Q.|last4=Zhang|first4=S. J.|last5=Lv|first5=Y. X.|last6=Zhu|first6=J. L.|last7=Yu|first7=R. C.|last8=Jin|first8=C. Q.|title=A new "111" type iron pnictide superconductor LiFeP|journal=EPL|volume=87|issue=3|year=2009|page=37004|doi=10.1209/0295-5075/87/37004|bibcode=2009EL.....8737004D|arxiv=0908.4043|s2cid=119227185}}</ref> Doping or applied pressure will transform the compounds into superconductors.<ref name=r1/><ref>{{cite journal|title = Iron-based superconductors|author = Day, C. |year = 2009|pages = 36–40|volume = 62|issue = 8 |journal = Physics Today|doi=10.1063/1.3206093|bibcode = 2009PhT....62h..36D |doi-access = free}}</ref><ref>{{cite journal|title = Superconductivity in iron compounds |author = Stewart, G. R. |year = 2011|pages = 1589–1652|volume = 83|issue = 4 |journal = Rev. Mod. Phys.|doi=10.1103/revmodphys.83.1589|bibcode = 2011RvMP...83.1589S |arxiv = 1106.1618|s2cid = 119238477 }}</ref>

Compounds such as Sr<sub>2</sub>ScFePO<sub>3</sub> discovered in 2009 are referred to as the '42622' family, as FePSr<sub>2</sub>ScO<sub>3</sub>.<ref>{{cite journal | doi=10.1088/0953-2048/23/2/022001 | title=Evidence for nodal superconductivity in Sr2ScFePO3 | year=2010 | last1=Yates | first1=K A | last2=Usman | first2=I T M | last3=Morrison | first3=K | last4=Moore | first4=J D | last5=Gilbertson | first5=A M | last6=Caplin | first6=A D | last7=Cohen | first7=L F | last8=Ogino | first8=H | last9=Shimoyama | first9=J <!--exactly 9 authors--> | journal=Superconductor Science and Technology | volume=23 | issue=2 | page=022001 | arxiv = 0908.2902 | bibcode = 2010SuScT..23b2001Y| s2cid=119248392 }}</ref> Noteworthy is the synthesis of (Ca<sub>4</sub>Al<sub>2</sub>O<sub>6−y</sub>)(Fe<sub>2</sub>Pn<sub>2</sub>) (or Al-42622(Pn); Pn = As and P) using high-pressure synthesis technique. Al-42622(Pn) exhibit superconductivity for both Pn = As and P with the transition temperatures of 28.3 K and 17.1 K, respectively. The a-lattice parameters of Al-42622(Pn) (a = 3.713 Å and 3.692 Å for Pn = As and P, respectively) are smallest among the iron-pnictide superconductors. Correspondingly, Al-42622(As) has the smallest As-Fe-As bond angle (102.1°) and the largest As distance from the Fe planes (1.5 Å).<ref name=shirage1/> High-pressure technique also yields (Ca<sub>3</sub>Al<sub>2</sub>O<sub>5−y</sub>)(Fe<sub>2</sub>Pn<sub>2</sub>) (Pn = As and P), the first reported iron-based superconductors with the perovskite-based '32522' structure. The transition temperature (T<sub>c</sub>) is 30.2 K for Pn = As and 16.6 K for Pn = P. The emergence of superconductivity is ascribed to the small tetragonal a-axis lattice constant of these materials. From these results, an empirical relationship was established between the a-axis lattice constant and T<sub>c</sub> in iron-based superconductors.<ref name=shirage2/>

In 2009, it was shown that undoped iron pnictides had a magnetic quantum critical point deriving from competition between electronic localization and itinerancy.<ref>{{Cite journal|last1=Dai|first1=Jianhui|last2=Si|first2=Qimiao|last3=Zhu|first3=Jian-Xin|last4=Abrahams|first4=Elihu|date=2009-03-17|title=Iron pnictides as a new setting for quantum criticality|journal=Proceedings of the National Academy of Sciences|language=en|volume=106|issue=11|pages=4118–4121|doi=10.1073/pnas.0900886106|issn=0027-8424|pmc=2657431|pmid=19273850|arxiv=0808.0305|bibcode=2009PNAS..106.4118D|doi-access=free}}</ref>

[[File:Phase diagram of the 122 family of ferro-pnictides.png|thumb|right|300px|Phase diagram of the 122 family of ferro-pnictides complemented by the 122(Se) family as a generalized phase diagram for the iron based superconductors.<ref name="Kordyuk2012">{{Cite journal|author=A. A. Kordyuk |year=2012 |title=Iron-based superconductors: Magnetism, superconductivity, and electronic structure (Review Article) |journal=Low Temp. Phys. |volume=38 |issue=9 |arxiv=1209.0140|bibcode=  2012LTP....38..888K|doi=10.1063/1.4752092 |page=888 |s2cid=117139280 }}</ref>]]

==Phase diagrams==
Similarly to superconducting cuprates, the properties of iron based superconductors change dramatically with doping. Parent compounds of FeSC are usually metals (unlike the cuprates) but, similarly to cuprates, are ordered [[Physics:Antiferromagnetism|antiferromagnetically]] that often termed as a spin-density wave (SDW). The [[Physics:Superconductivity|superconductivity]] (SC) emerges upon either hole or electron doping. In general, the [[Phase diagram|phase diagram]] is similar to the cuprates.<ref name="Kordyuk2012"/>

==Superconductivity at high temperature==
{{Main|Physics:High-temperature superconductivity}}
[[File:Fephasediag.png|thumb|300px|Simplified doping dependent phase diagrams of iron-based superconductors for both Ln-1111 and Ba-122 materials. The phases shown are the antiferromagnetic/[[spin density wave]] (AF/SDW) phase close to zero doping and the superconducting phase around optimal doping. The Ln-1111 phase diagrams for La<ref name=Luet2008>
{{cite journal
 |year=2009
 |title=Electronic phase diagram of the LaO<sub>1−x</sub>F<sub>x</sub>FeAs superconductor
 |journal=Nature Materials
 |volume=8|issue=4|doi=10.1038/nmat2397
 |pmid=19234445
 |bibcode=2009NatMa...8..305L
 |pages=305–9
|arxiv=0806.3533 |last1=Luetkens
 |first1=H
 |last2=Klauss
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 |last3=Kraken
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 |last5=Dellmann
 |first5=T
 |last6=Klingeler
 |first6=R
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 |last8=Khasanov
 |first8=R
 |last9=Amato
 |first9=A
 |last10=Baines
 |first10=C
 |last11=Kosmala
 |first11=M
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 |last13=Braden
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 |last15=Leps
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 |s2cid=14660470
 }}</ref> and Sm<ref name=Drew2008>
{{cite journal
 |year=2009
 |title=Coexistence of static magnetism and superconductivity in SmFeAsO<sub>1−x</sub>F<sub>x</sub> as revealed by muon spin rotation
 |journal=[[Physics:Nature Materials|Nature Materials]]
 |volume=8 |issue=4 |pages=310–314
 |doi=10.1038/nmat2396
 |pmid=19234446
|bibcode=2009NatMa...8..310D
|arxiv=0807.4876 |last1=Drew
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 }}</ref><ref name=Sann2009>
{{cite journal|doi=10.1103/PhysRevB.80.052503
 |year=2009
 |title=Competition between magnetism and superconductivity at the phase boundary of doped SmFeAsO pnictides
 |journal=Physical Review B
 |volume=80
 |issue=5
 |page=052503
 |arxiv=0902.2156
|last1=Sanna
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 |s2cid=119247319
 }}</ref> were determined using [[Physics:Muon spin spectroscopy|muon spin spectroscopy]], the phase diagram for Ce<ref name=Zhao2008>
{{cite journal
 |year=2008
 |title=Structural and magnetic phase diagram of CeFeAsO<sub>1−x</sub>F<sub>x</sub> and its relation to high-temperature superconductivity
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 |volume=7 |issue=12 |pages=953–959
 |doi=10.1038/nmat2315
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|bibcode=2008NatMa...7..953Z
|arxiv=0806.2528 |last1=Zhao
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 }}</ref> was determined using [[Physics:Neutron diffraction|neutron diffraction]]. The Ba-122 phase diagram is based on.<ref name=Chu2008>
{{cite journal
 |year=2009
 |doi=10.1103/PhysRevB.79.014506
 |title=Determination of the phase diagram of the electron doped superconductor Ba(Fe<sub>1−x</sub>Co<sub>x</sub>)<sub>2</sub>As<sub>2</sub>
|journal=Physical Review B
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 }}</ref>]]

Superconducting transition temperatures are listed in the tables (some at high pressure). BaFe<sub>1.8</sub>Co<sub>0.2</sub>As<sub>2</sub> is predicted to have an upper critical field of 43 [[Tesla (unit)|tesla]] from the measured coherence length of 2.8&nbsp;nm.<ref name=Yin/>

In 2011, Japanese scientists made a discovery which increased a metal compound's superconductivity by immersing iron-based compounds in hot alcoholic beverages such as red wine.<ref>{{cite web|title=Press release: Japanese scientists use alcoholic drinks to induce superconductivity|url=http://www.iop.org/news/11/march/page_50051.html|publisher=Institute of Physics|date=7 March 2011}}</ref><ref>{{cite journal|last1=Deguchi|first1=K|last2=Mizuguchi|first2=Y|last3=Kawasaki|first3=Y|last4=Ozaki|first4=T|last5=Tsuda|first5=S|last6=Yamaguchi|first6=T|last7=Takano|first7=Y|title=Alcoholic beverages induce superconductivity in FeTe<sub>1−x</sub>S<sub>x</sub>|journal=Superconductor Science and Technology|volume=24|issue=5|year=2011|page=055008|arxiv=1008.0666|doi=10.1088/0953-2048/24/5/055008|bibcode=2011SuScT..24e5008D|s2cid=93508333}}</ref> Earlier reports indicated that excess Fe is the cause of the bicollinear antiferromagnetic order and is not in favor of superconductivity. Further investigation revealed that weak acid has the ability to deintercalate the excess Fe from the interlayer sites. Therefore, weak acid annealing suppresses the antiferromagnetic correlation by deintercalating the excess Fe and, hence superconductivity is achieved.<ref>{{cite news|title=Red Wine, Tartaric Acid, and the Secret of Superconductivity|url=https://www.technologyreview.com/s/427302/red-wine-tartaric-acid-and-the-secret-of-superconductivity/|work=MIT Technology Review|date=March 22, 2012|language=en}}</ref><ref>{{cite journal|last1=Deguchi|first1=K|last2=Sato|first2=D|last3=Sugimoto|first3=M|last4=Hara|first4=H|last5=Kawasaki|first5=Y|last6=Demura|first6=S|last7=Watanabe|first7=T|last8=Denholme|first8=S J|last9=Okazaki|first9=H|last10=Ozaki|first10=T|last11=Yamaguchi|first11=T|last12=Takeya|first12=H|last13=Soga|first13=T|last14=Tomita|first14=M|last15=Takano|first15=Y|title=Clarification as to why alcoholic beverages have the ability to induce superconductivity in Fe<sub>1+d</sub>Te<sub>1−x</sub>S<sub>x</sub>|journal=Superconductor Science and Technology|volume=25|issue=8|year=2012|page=084025|arxiv=1204.0190|doi=10.1088/0953-2048/25/8/084025|bibcode=2012SuScT..25h4025D|s2cid=119223257}}</ref>

There is an empirical correlation of the transition temperature with [[Physics:Electronic band structure|electronic band structure]]: the T<sub>c</sub> maximum is observed when some of the [[Physics:Fermi surface|Fermi surface]] stays in proximity to [[Biography:Ilya Lifshitz|Lifshitz]] topological transition.<ref name="Kordyuk2012"/> Similar correlation has been later reported for [[Physics:Cuprate superconductor|high-T<sub>c</sub> cuprates]] that indicates possible similarity of the superconductivity mechanisms in these two families of high temperature superconductors.<ref name="Kordyuk2018">{{Cite journal|author=A. A. Kordyuk |year=2018 |title=Electronic band structure of optimal superconductors: from cuprates to ferropnictides and back again (Review Article) |journal=Low Temp. Phys. |volume=44 |issue=6 |arxiv=1803.01487|bibcode=  2018LTP....44..477K|doi=10.1063/1.5037550 |pages=477–486|s2cid=119342977 }}</ref>

===Thin films===

The critical temperature is increased further in thin-films of iron chalcogenides on suitable substrates. In 2015, a T<sub>c</sub> of around 105-111 K was observed in thin films of iron selenide grown on [[Chemistry:Strontium titanate|strontium titanate]].<ref name = Ge2014>{{cite journal|last1=Ge|first1=JF|last2=Liu|first2=ZL|last3=Liu|first3=C|last4=Gao|first4=CL|last5=Qian|first5=D|last6=Xue|first6=DK|last7=Liu|first7=Y|last8=Jia|first8=JF|title=Superconductivity above 100K in single-layer FeSe films on doped SrTiO3|journal=Nat. Mater.|volume=14|pages=285–9|year=2014|issue=3 |doi=10.1038/NMAT4153|pmid=25419814 |arxiv=1406.3435 |s2cid=119227626 }}</ref>

==See also==
{{div col|colwidth=22em}}
*[[Chemistry:Charge-transfer complex|Charge-transfer complex]]
*[[Physics:Color superconductivity|Color superconductivity]] in quarks
*[[Physics:Kondo effect|Kondo effect]]
*[[Physics:Magnetic sail|Magnetic sail]]
*[[Organization:National Superconducting Cyclotron Laboratory|National Superconducting Cyclotron Laboratory]]
*[[Physics:Spallation Neutron Source|Spallation Neutron Source]]
*[[Physics:Superconducting radio frequency|Superconducting radio frequency]]
*[[Physics:Superfluid film|Superfluid film]]
*[[Engineering:Timeline of low-temperature technology|Timeline of low-temperature technology]]
{{div col end}}

==References==
{{Reflist|30em}}


[[Category:Superconductors]]
[[Category:Iron compounds]]

{{Sourceattribution|Iron-based superconductor}}