Iron chalcogenides are of great interest because they have the simplest structure in the Fe based superconductor family, and show low anisotropies, high upper critical fields and high critical current densities. These compounds can, therefore, be considered as reference materials to study the behaviour of all layered Fe based superconductors, both to advance fundamental physical understanding and to explore potential high field applications. Research carried out since the discovery of superconductivity in these iron chalcogenides in 2008 is reviewed to explore the effects of key parameters such as structure, stoichiometry, pressure, elemental substitutions and strain on superconductivity. The effect of these parameters on the superconducting transition temperature of Fe1+ySe and Fe1+yTe1−xSex materials is critically assessed and the published results compared in an attempt to elucidate the relationship between structural parameters and superconducting properties in these compounds. Challenges for future work are identified.
LeePJ: ‘Engineering superconductivity 2001: New York’; 2001, Chichester, Wiley-Interscience.
3.
SchriefferJR: ‘Theory of superconductivity’; 1999, Reading, MA, Perseus Books.
4.
BednorzJG and MiillerKA: ‘Possible high Tc superconductivity in the Ba-La-Cu-O system’, Phys. B: Condens. Matter, 1986, B64, 189–193.
5.
WuMK, AshburnR, TorngC, HorPH, MengRL, GaoL, HuangZJ, WangYQ and ChuW: ‘Superconductivity at 93 K in a new mixed-phase Y–Ba–Cu–O compound system at ambient pressure’, Phys. Rev. Lett., 1987, 58, (9), 908.
6.
MaedaH, TanakaY, FukutomiM and AsanoT: A new high-Tc oxide superconductor without a rare earth element’,Jpn J. Appl. Phys., 1988, 27, (2), L209.
7.
MaenoY, HashimotoH, YoshidaK, NishizakiS, FujitaT, BednorzJG and LichtenbergF: ‘Superconductivity in a layered perovskite without copper’, Nature, 1994, 372, 532.
8.
HiroiZ, YonezawaS and MuraokaY: ‘Unprecedented superconductivity in β-pyrochlore osmate KOs2O6’, J. Phys. Soc. Jpn, 2004, 73, 1651.
9.
TakadaK, SakuraiH, Takayama-MuromachiE, IzumiF, DilanianRA and SasakiT: ‘Superconductivity in two-dimensional CoO2 layers’, Nature, 2003, 422, 53.
10.
ShirotaniI, ShimayaY, KihouK, SekineC, TakedaN, IshikawaM and YagiT: ‘Superconductivity of new filled skutterudite YFe4P12 prepared at high pressure’, J. Phys.: Condens. Matter, 2003, 15, (28), S2201.
11.
MeisnerGP: ‘Superconductivity and magnetic order in ternary rare earth transition metal phosphides’, Phys. B, 1981, 108B, 763.
12.
CrabtreeG, GreeneL and JohnsonP: ‘Celebrating 100 years of superconductivity: special issue on the iron-based superconductors’, Rep. Progr. Phys., 2011, 74, (12).
13.
LiQ, SiWD and DimitrovI: ‘Films of iron chalcogenide superconductors’, Rep. Progr. Phys., 2011, 74, 124510.
14.
BraithwaiteD, LapertotG, KnafoW and SheikinI: ‘Evidence for anisotropic vortex dynamics and Pauli limitation in the upper critical field of FeSe1-xTex’, J. Phys. Soc. Jpn, 2010, 79, 0537703.
15.
TakanoY: ‘Focus on superconducting properties of iron chalcogenides FOREWORD’, Sci. Technol. Adv. Mater., 2012, 13, (5).
16.
KamiharaY, HiramatsuH, HiranoM, KawamuraR, YanagiH, KamiyaT and HosonoH: ‘Iron-based layered superconductor: LaOFeP’, J. Am. Chem. Soc., 2006, 128, 10012–10013.
17.
Zhi-AnR: ‘Superconductivity at 55 K in iron-based f-doped layered quaternary compound Sm[O1−xFx]−FeAs’, Chin. Phys. Lett., 2008, 2, 25.
18.
ChenGF, LiZ, WuD, LiG, HuWZ, DongJ, ZhengP, LuoJL and WangNL: ‘Superconductivity at 41 K and its competition with spin- density-wave instability in layered CeOl−xFxFeAs’, Europhys. Lett., 2008, 109.
19.
RenZA, YangJ and LuW: ‘Superconductivity at 52 K in iron based F doped layered quaternary compound Pr[Ol−xFx]FeAs’, Mater. Res. Innov., 2008, 12, 105.
20.
RotterM, TegelM, SchellenbergI, HermesW, PottgenR and JohrendtD: ‘Spin-density-wave anomaly at 140 K in the ternary iron arsenide BaFe2As2’, Phys. Rev. B, 2008, 78B, 020503.
21.
WangXC, LiuQQ, LvYX, GaoWB, YangLX, YuRC, LiFY and JinCQ: ‘The superconductivity at 18 K in LiFeAs system’, Solid State Commun., 2008, 148, 538.
22.
LennieAR, RedfernSAT, SchofieldPF and VaughanDJ: ‘Synthesis and Rietveld refinement of mackinawite, tetragonal FeS’, Mineral. Magaz., 1995, 59, 677.
23.
HsuFC, LuoJY, YehKW, ChenTK, HuangTW, WuPM, LeeYC, HuangYL, ChuYY, YanDC and WuMK: ‘Superconductivity in the PbO-type structure a-FeSe’, Proc. National Acad. Sci., 2008, 105, (38), 14262.
24.
McQueenTM, HuangQ, KsenofontovV, FelserC, XuQ, ZandbergenH, HorYS, AllredJ, WilliamsAJ, QuD, CheckelskyJ and CavaRJ: ‘Extreme sensitivity of superconductivity to stoichiometry in FeSe’, Phys. Rev. B, 2009, 79B, 014522.
25.
IshidaK, NakaiY and HosonoH: ‘To what extent iron-pnictide new superconductors have been clarified: a progress report’, J. Phys. Soc. Jpn, 2009, 78, (6), 062001.
26.
SubediA, ZhangL, SinghDJ and DuMH: ‘Density functional study of FeS, FeSe, and FeTe: electronic structure, magnetism, phonons, and superconductivity’, Phys. Rev. B, 2008, 78, 134514
27.
SiW, LinZW, JieQ, YinWG, ZhouJ, GuG and JohnsonPD: ‘Enhanced superconducting transition temperature in FeSe0·5Te0·5 thin films’, Appl. Phys. Lett., 2009, 95, (5), 2504.
28.
WangQY, LiZ, ZhangWH, ZhangZC, ZhangJS, LiW, DingH, OuYB, DengP, ChangK, WenJ, SongCL, HeK, JiaJF, JiSH, WangY, WangL, ChenX, MaX and XueQK: ‘Interface-induced high-temperature superconductivity in single unit-cell FeSe films on SrTiO3’, Chin. Phys. Lett., 2012, 29, (3), 037402.
29.
SefatAS, HuqA and McGuireMA: ‘Superconductivity in Co-doped LaFeAsO’, Phys. Rev. B, 2008, 78B, (10), 4505.
CaoG, WangC, ZhuZ, JiangS, LuoY, ChiS, RenZ, TaoQ, WangY and XuZ: ‘Superconductivity induced by cobalt doping in iron-based’, Phys. Rev. B, 2009, 79B, 054521.
32.
YehKW, HuangTW and HuangY: ‘Tellurium substitution effect on superconductivity of the alpha-phase iron selenide’, Europhys. Lett., 2008, 84, (3), 14.
33.
YehKW, HsuHC, HuangTW, WuPM, HuangYL, ChenTK, LuoJY and WuMK: ‘Se and Te doping study of the FeSe superconductors’, J. Phys. Soc. Jpn, 2008, (77), 19–22.
34.
MargadonnaS, TakabayashiY, McDonaldMT, KasperkiewiczK, MizuguchiY, TakanoY, FitchAN, SuardE and PrassidesK: ‘Crystal structure of the new FeSe superconductor’, Chem. Commun. (Cambridge), 2008, 43, 5607.
35.
WuaMK, HsuFC, YehKW, HuangTW, LuoJY, WangMJ, ChangHH, ChenTK, RaoSM, MokBH, ChenCL, HuangYL, KeCT, WuPM, ChangAM, WuCT and PerngTP: ‘The development of the superconducting PbO-type b-FeSe and related compounds’, Phys. C, 2009, 469C, 340–349.
36.
MizuguchiY, TomiokaF, TsudaSh, YamaguchiT and TakanoY: ‘Substitution effects on FeSe superconductor’, J. Phys. Soc. Jpn, 2009, 78, 074712.
37.
WangMJ, LuoJY, HuangTW, ChangHH, ChenTK, HsuFC, WuCT, WuPM, ChangAM and WuMK: ‘Crystal orientation and thickness dependence of the superconducting transition temperature of tetragonal FeSe1−x thin films’, Phys. Rev. Lett., 2009, 103, (11), 7002.
38.
MalavasiL and MargadonnaS: ‘Structure–properties correlations in Fe chalcogenide superconductors’, Chem. Soc. Rev., 2012, 41, 3897–3911.
39.
McQueenTM, WilliamsAJ, StephensPW, TaoJ, ZhuY, KsenofontovV, CasperF, FelserC and CavaRJ: ‘Tetragonal-to-orthorhombic structural phase transition at 90 K in the superconductor Fe1·01Se’, Phys. Rev. Lett., 2009, 103, 057002.
40.
ImaiY, TanakaR, AkiikeT, HanawaM, TsukadaIT and MaedaA: ‘Superconductivity of FeSe1-xTex thin films grown by pulsed laser deposition’, Jpn J. Appl. Phys., 2010, 49, (2), 023101-023101-5.
41.
ImaiIY, TakanoriT, HanawaM, TsukadaI, IchinoseA, MaedaA, HikageT, KawaguchiT and KutaH: ‘Systematic comparison of eight substrates in growth of FeSe0·5Te0·5 superconducting thin films’, Appl. Phys. Expr., 2010, 3, 043102.
42.
BellingeriE, PallecchiI, BuzioR, GerbiA, MarreD, CimberleMR, TropeanoM, PuttiM, PalenzonaA and FerdeghiniC: ‘TC = 21K in epitaxial FeSe0·5Te0·5 thin films with biaxial compressive strain’, Appl. Phys. Lett., 2010, 96, (10), 2512.
43.
BellingeriE, BuzioR, GerbiA, MarreD, CongiuS, CimberleMR, TropeanoM, SiriAS, PalenzonaA and FerdeghiniC: ‘High quality epitaxial FeSe0·5Te0·5 thin films grown on SrTiO3 substrates by pulsed laser deposition’, Supercond. Sci. Technol., 2009, 22, (10), 5007.
44.
ViennoisaR, GianniniaE, MarelaD and CernyR: ‘Effect of Fe excess on structural, magnetic and superconducting properties of single-crystalline Fe1+xTe1-ySey’, J. Solid State Chem., 2010, 183, (4), 769–775.
45.
JourdanM and HaafS: ‘Preparation, characterization, and upper critical field of epitaxial FeSe thin films’, J. Appl. Phys., 2010, 108, 023913.
46.
FangMH, PhamHM, QianB, LiuTJ, VehstedtEK, LiuY, SpinuL and MaoZQ: ‘Superconductivity close to magnetic instability in Fe(Se1-xTex)0·82’, Phys. Rev. B, 2008, 78B, 224503.
47.
NieYF, BrahimiE, BudnickJI, HinesWA, JainM and WellsBO: ‘Suppression of superconductivity in FeSe films under tensile strain’, Appl. Phys. Lett., 2009, 94, (24), 2505.
48.
XiaY, HuangF, XieX and JiangM: ‘Preparation and superconductivity of stoichiometric β-FeSe’, Europhys. Lett., 2009, 86, 37008.
49.
ShipraR, TakeyaH, HirataK and SundaresanA: ‘Effects of Ni and Co doping on the physical properties of tetragonal FeSe0·5Te0·5 superconductor’, Phys. C, 2010, 470, 528.
HuangSX, ChienCL, ThampyV and BroholmC: ‘Control of tetrahedral coordination and superconductivity in FeSe0·5Te0·5 thin films’, Phys. Rev. Lett., 2010, 104, 217002.
52.
HanY, LiWY, CaoLX, ZhangS, XuB and ZhaoBR: ‘Preparation and superconductivity of iron selenide thin films’, J. Phys.: Condens. Matter, 2009, 21, (23), 5702.
53.
HoriganeK, HirakaH and OhoyamaK: ‘Relationship between structure and superconductivity in FeSe1−xTex’, J. Phys. Soc. Jpn, 2009, 78, (7).
54.
ChenL, TsaiCF, ZhuY, BiZh and WangH: ‘Enhanced superconducting properties in epitaxial FeSe thin films with self-assembled Fe3O4 nanoparticles’, Phys. C, 2011, 471C, 515.
55.
TsukadaI, HanawaM, AkiikeT, NabeshimaF, ImaiY, IchinoseA, KomiyaS, HikageT, KawaguchiT, IkutaH and MaedaA: ‘Epitaxial growth of FeSe0.5Te0.5 thin films on CaF2 substrates with high critical current density’, Appl. Phys. Expr., 2011, 4, 053101.
56.
HanawaM, IchinoseA, KomiyaS, TsukadaI, AkiikeT, ImaiY, HikageT, KawaguchiT, IkutaH and MaedaA: ‘Substrate dependence of structural and transport properties in FeSe0·5Te0·5 thin films’, Jpn J. Appl. Phys., 2011, 50, 053101.
57.
SpellerSC, AksoyC, SaydamM, TaylorH, BurnellG, BoothroydAT and GrovenorCRM: ‘Analysis of FeySe1−xTex thin films grown by radio frequency sputtering’, Supercond. Sci. Technol., 2011, 24, 075023.
58.
YehKW, KeCT, HuangTW, ChenTK, HuangYL, WuPM and WuMK: ‘Superconducting FeSe1-xTex single crystals grown by optical zone-melting technique’, Cryst. Growth Des., 2009, 9, 4847.
59.
GuntherA, DeisenhoferJ, KantC, Krug von NiddaH and TsurkanV: ‘Improvement of superconducting properties of FeSe0·5Te0·5 single crystals by Mn substitution’, Supercond. Sci. Technol., 2011, 24, 045009.
60.
TsurkanV, DeisenhoferJ, GuntherA, KantCh, KlemmM, Krug von NiddaH.-A, SchrettleF and LoidlA: ‘Physical properties of FeSe0·5Te0·5 single crystals grown under different conditions’, Eur. Phys. J. B, 2011, 79B, 289.
61.
TegelM, LohnertC and JohrendtD: ‘The crystal structure of FeSe0·44Te0·56’, Solid State Commun., 2010, 150, 383.
62.
SiWD, HanSJ, ShiXY, EhrlichSN, JaroszynskiJ, GoyalA and LiQ: ‘High current superconductivity in FeSe0.5Te0.5-coated conductors at 30 tesla’, Nature Commun., 2013, 4, 1–5.
63.
SalesBC, SefatAS, McGuireMA, JinRY, MandrusD and MozharivskyY: ‘Bulk superconductivity at 14 K in single crystals of Fe1+yTexSe1−x’, Phys. Rev. B, 2009, 79B, (9), 4521.
64.
NabeshimaF, ImaiY, HanawaM, TsukadaI and MaedaA: ‘Enhancement of the superconducting transition temperature in FeSe epitaxial thin films by anisotropic compression’, Appl. Phys. Lett., 2013, 103, (17), 172602.
65.
BracciniV, KawaleS, ReichE, BellingeriE, PellegrinoL, SalaA, PuttiM, HigashikawaK, KissT, HolzapfelB and FerdeghiniC: ‘Highly effective and isotropic pinning in epitaxial Fe(Se,Te) thin films grown on CaF2 substrates’, Appl. Phys. Lett., 2013, 103, (17), 172601.
66.
SpellerSC, BrittonTB, HughesG, Lozano-PerezS, BoothroydAT, PomjakushinaE, ConderK and GrovenorCRM: ‘Analysis of local chemical and structural inhomogeneities in FeySe1−xTex single crystals’, Appl. Phys. Lett., 2011, 99, (19), 192504.
LiuTJ, KeX, QianB, HuJ, FobesD, VehstedtEK, PhamH, YangJH, FangMH, SpinuL, SchifferP, LiuY, and MaoZQ: ‘Charge-carrier localization induced by excess Fe in the superconductor Fe1+yTe1−xSex’, Phys. Rev. B, 2009, 80B, 174509.
69.
MargadonnaS, TakabayashiY, OhishiY, MizuguchiY, TakanoY, KagayamaT, NakagawaT, TakataM and PrassidesK: ‘Pressure evolution of the low-temperature crystal structure and bonding of the superconductor FeSe (Tc = 37K)’, Phys. Rev. B, 2009, 80B, (6), 4506.
70.
MizuguchiY and TakanoY: ‘A review of Fe-chalcogenide superconductors: the simplest Fe-based superconductor’, J. Phys. Soc. Jpn, 2010, 79, 102001.
71.
KurokiK, UsuiH, OnariS, AritaR and AokiH: ‘Pnictogen height as a possible swtich between high Tc nodeless and low Tc nodal pairings in the iron based superconductors’, Phys. Rev. B, 2009, 79, 224511.
72.
ImaiT, AhilanK, NingFL, McQueenTM and CavaRJ: ‘Why does undoped FeSe become a high-Tc superconductor under pressure?’, Phys. Rev. Lett., 2009, 102, 177005.
73.
MizuguchiY, TomiokaF and TsudaS: ‘Superconductivity at 27 K in tetragonal FeSe under high pressure’, Appl. Phys. Lett., 2008, 93, 152505.
74.
TakahashiH, OkadaH, IgawaK, KamiharaY, HiranoM, HosonoH, MatsubayashiK and UwatokoY: ‘High-pressure studies on superconductivity in LaFeAsO1−xFx and SmFeAsO1−xFx’, J. Supercond. Novel Mag., 2009, 22, (6), 595.
75.
GarbarinoG, SowA, LejayP, SulpiceA, ToulemondeP, CrichtonW, MezouarM and Nunez-RegueiroM: ‘High temperature superconductivity (Tc onset at 34K) in the high pressure orthorhombic phase of FeSe’, Europhys. Lett., 2009, 86, 27001.
76.
SefatAS: ‘Pressure effects on two superconducting iron-based families’, Rep. Progr. Phys., 2011, 74, (12), 124502.
77.
MedvedevS, McQueenTM, TroyanIA, PalasyukT, EremetsMI, CavaRJ, NaghaviS, CasperF, KsenofontovV, WortmannG and FelserC: ‘Electronic and magnetic phase diagram of β-Fe1·01Se with superconductivity at 36·7 K under pressure’, Nature Mater., 2009, 8, 630.
78.
TanSY, ZhangY, XiaM, YeZR, ChenF, XieX, PengR, XuDF, FanQ, XuHC, JiangJ, ZhangT, LaiXC, XiangT, HuJP, XieBP and FengDL: ‘Interface-induced superconductivity and strain-dependent spin density waves in FeSe/SrTiO3 thin films’, Nature Mater., 2013, 12, (7), 634–640.
79.
AwanaVPS, PalA, VajpayeeA, MeenaRS, KishanH, HusainM, ZengR, YuS, YamauraK and Takayama-MuromachiE: ‘Superconductivity in SmFe1-xCoxAsO (x = 0·0-0·30)’, J. Appl. Phys., 2010, 107, (9), 09E146.
80.
HoriganeK, HirakaH and OhoyamaK: ‘Relationship between structure and superconductivity in FeSe1-xTex’, J. Phys. Soc. Jpn, 2009, 78, (7), 074718.
LeiH, WangK, HuR, RyuH, AbeykoonM, BozinE and PetrovicC: ‘Iron chalcogenide superconductors at high magnetic fields’, Sci. Technol. Adv. Mater., 2012, 13, (05), 4305.
83.
GrestyNC, TakabayashiY, GaninAY, McDonaldT, ClaridgeB, GiapD, MizuguchiY, TakanoY, KagayamaT, OhishiY, TakataM, RosseinskyMJ, MargadonnaS and PrassidesK: ‘Structural phase transitions and superconductivity in Fe1+δSe0·57Te0·43 at ambient and elevated pressures’, J. Am. Chem. Soc., 2009, 131, 16944.
84.
SpellerSC, BrittonTB, HughesGM, Krzton-MaziopaA, PomjakushinaE, ConderK, BoothroydAT and GrovenorCRM: ‘Microstructural analysis of phase separation in iron chalcogenide superconductors’, Supercond. Sci. Technol., 2012, 25, (8), 084023.
85.
HanY, LiWY, CaoLX, WangXY, XuB, ZhaoBR, GuoYQ and YangZL: ‘Superconductivity in iron telluride thin films under tensile stress’, Phys. Rev. Lett., 2010, 104, (1), 7003.
86.
AgatsumaS, YamagishiT, TakedaS and NaitoM: ‘MBE growth of FeSe and Sr1−xKxFe2As2’, Phys. C: Supercond., 2010, 470, (20), 1468–1472.
87.
SpellerS: ‘Microstructural development and control in Ti2Ba2CaCu2O8 Materials Department report, Oxford University, UK, 2004.
88.
HanawaM, IchinoseA, KomiyaS, TsukadaI, ImaiY and MaedaA: ‘Empirical selection rule of substrate materials for iron chalcogenide superconducting thin films’, Jpn J. Appl. Phys., 2012, 51, (1), 010104.
89.
IidaK, HanischJ, SchulzeM, AswarthamS, WurmehlS, BuchnerB, SchultzL and HolzapfelB: ‘Generic Fe buffer layers for Fe-based superconductors: epitaxial FeSe1−xTex thin films’, Appl. Phys. Lett., 2011, 99, (20), 202503.
90.
GeorgeJ and PradeepB: ‘Preparation and properties of co-evaporated bismuth telluride Bi2Te3 thin films’, Solid State Commun., 1985, 56, (1), 117.
91.
CharlesE, GroubertE, BoyerAM, CampbellA, BluntFJ, JohnsonJD and FreemanPA: ‘Structural and electrical properties of Bismuth Telluride films grown by the molecular beam technique’, J. Appl. Phys., 1988, 73, 1252.
92.
StolzerM, BecksteinV and MeuselJ: ‘Deposition of (Bi,Sb)2Te3 films by magnetron co-sputtering from two targets’, Proc. 15th Int. Conf. on ‘Thermoelectrics’, Pasadena, CA, USA, March 1996, Jet Propulsion Lab., California Inst. of Tech., Pasadena, CA, USA, 422.
