FeSe超导单晶综述

arXiv:1104.0695v1[cond-mat.supr-con]4Apr2011REVIEWARTICLESinglecrystalgrowthandpropertiesofiron-chalcogenidesuperconductorsJinshengWen1,2,3,GuangyongXu2,GendaGu2,J.M.Tranquada2andR.J.Birgeneau1,31PhysicsDepartment,UniversityofCalifornia,Berkeley,California94720,USA2CondensedMatterPhysicsandMaterialsScienceDepartment,BrookhavenNationalLaboratory,Upton,NewYork11973,USA3MaterialsScienceDivision,LawrenceBerkeleyNationalLaboratory,Berkeley,California94720,USAE-mail:[e-mail],[e-mail],wepresentasummaryoftheresultsonsinglecrystalgrowthandcharacterizationoftwotypesofiron-chalcogenidesuperconductors,Fe1+yTe1−xSex(11),andAxFe2−ySe2(A=K,Rb,Cs,Tl,Tl/K,Tl/Rb),usingBridgman,zone-melting,vaporself-transport,andfluxtechniques.Itwillbeshownthatforthe11system,whilestaticmagneticorderaroundthereciprocallatticeposition(0.5,0)competeswithsuperconductivity,spinexcitationscenteredaround(0.5,0.5)arecloselycoupledtothematerials’superconductivity;thisismadeevidentbythestrongcorrelationbetweenthespectralweightaround(0.5,0.5)andthesuperconductingvolumefraction.Theobservationofaspinresonancebelowthesuperconductingtemperature,Tc,andthemagnetic-fielddependenceoftheresonance,emphasizetheimportantrolespinexcitationsplayinthesuperconductivity.Generally,theseresultsillustratethesimilaritiesbetweentheiron-basedandcupratesuperconductors.InAxFe2−ySe2,superconductivitywithTc∼30Kbordersanantiferromagneticinsulatingphase;thisisclosertothebehaviorobservedinthecupratesbutdiffersfromthatinotheriron-basedsuperconductors.Contents1Introduction32Crystalgrowth52.1Bridgmanmethod...............................52.2Opticalzone-meltingtechnique.......................62.3Vaporself-transportandfluxmethod....................83Superconductivityinironchalcogenides83.1Superconductivityinthe11system.....................83.2Pressurestudyonthe11system.......................11CONTENTS23.3Dopingwith3dtransitionmetalsintoFe1+yTe1−xSex...........133.4SuperconductivityinAxFe2−ySe2(A=K,Rb,Cs,Tl,Tl/K,Tl/Rb)...133.5Summary...................................164Magneticcorrelations164.1Magneticorder................................164.1.1Fe1+yTe1−xSexsystem........................164.1.2AxFe2−ySe2materials.........................184.2SpinexcitationsinFe1+yTe1−xSex......................184.2.1Spindynamicsnear(0.5,0.5).....................184.2.2Dopingdependence..........................204.3Summary...................................225Conclusions236Acknowledgements24CONTENTS31.IntroductionAsuperconductingmaterialcanconductelectriccurrentwithzero-energylossduetotheabsenceofelectricalresistancebelowitssuperconductingtransitiontemperatureTc;suchbehaviorisclearlyofgreatpracticaluse[1].Onthetheoreticalside,superconductivitywasinitiallyunderstoodwiththeelegantmany-bodytheorydevelopedbyBardeen,Cooper,andSchrieffer,(BCStheory)[2];theseauthorsexplainedthephenomenonofsuperconductivityonthebasisofelectronpairswhoseinteractionismediatedbyelectron-phononcoupling.Inthe1980s,high-temperaturesuperconductivitywasdiscoveredinlamellarcopper-oxidematerialswhoseTccanbeaboveliquid-nitrogentemperature[3,4].Here,theelectron-phononcouplingasproposedinBCStheoryisnotsufficienttoinducesuperconductivityatsuchhightemperatures[5,6].Inthesecupratesuperconductingmaterials,superconductivitydevelopsfromelectronicallydopinganantiferromagneticMottinsulatingphasewithcarriers[5–9].Itisthushopedthatonemayeventuallyunderstandthehigh-Tcsuperconductivityintermsoftheinterplaybetweenmagnetismandsuperconductivity.Researchonhigh-Tcsuperconductivitygainednewmomentumintheyear2008withthediscoveryofiron-pnictidesuperconductors.TheinitialexcitementcamewiththediscoverybyHosono’sgroupofsuperconductivityinLaFeAsO1−xFx(labeled1111,basedontheelementalratiosinthechemicalformulaoftheparentmaterial)withTc=26K[10],followinganearlierreportbythesamegroupofsuperconductivityinLaFePO1−xFxwithTc∼5K[11].TheTcwassoonraisedto43K,eitherbyreplacingLawithSm(SmFeAsO1−xFx)[12],orbyapplyingpressure[13].Several1111superconductorswithTc50Khavebeensuccessivelyreported[14–17],andthecurrentrecordis56KinGd1−xThxFeAsO[17].Besidesthe1111system,threeotherfamiliesofiron-basedsuperconductorshavebeendiscovered,typifiedbyBaFe2As2(122)[18–21],LiFeAs(111)[22–28],andFe1+yTe1−xSex(11)[29–33].Theircrystalstructures,illustratedinfigure1,arealltetragonalatroomtemperature[11,26,34–37].Oneimportantcommonfeatureisthattheyarealllayeredstructures,asinthecuprates[5–9].Extensiveresearchhasbeencarriedouttostudythemagneticcorrelations.Itisnowwellestablishedforthesematerialsthatlong-rangeantiferromagneticorderissuppressedwithdoping,whilesuperconductivityappearsaboveacertaindopinglevel[35–56].Whilethereareafewcaseswheresuperconductivityappearssuddenlyaftermagneticorderdisappears[45],itismorecommonlyfoundthatmagneticorder,eithershort-orlong-ranged,coexistsinsomefashionwithsuperconductivityoverafiniterangeofdoping[44,46–50,52,54].Thefactthatsuperconductivitydevelopsconcomitantlywiththesuppressionofantiferromagneticorderiniron-basedsuperconductors[38,54,57