Background
Thediscoveryofsuperconductorsisinseparablefromlow-temperatureresearch.Inthe18thcentury,duetothelimitationsofcryogenictechnology,peoplethoughtthattherewere"permanentgases"thatcouldnotbeliquefied,suchashydrogen,helium,etc.In1898,theBritishphysicistDewarmadeliquidhydrogen.In1908,ProfessorKamerlinHonnesoftheLeidenCryogenicLaboratoryofLeidenUniversityintheNetherlandssuccessfullyliquefiedthelast"permanentgas"-helium,andobtained1.15-4.25byreducingthevaporpressureofliquidhelium.K'slowtemperature.Thebreakthroughinlow-temperatureresearchhaslaidthefoundationforthediscoveryofsuperconductors.
Attheendofthe19thcenturyandthebeginningofthe20thcentury,thereweredifferentopinionsaboutthechangeofmetalresistancenearabsolutezero.Oneviewisthattheresistanceofpuremetalsshoulddecreasewithdecreasingtemperatureanddisappearatabsolutezero.Anotherview,representedbyWilliamThomson(BaronKelvin),believesthatasthetemperaturedecreases,theresistanceofametalreachesaminimumvalueandbecomesinfiniteduetoelectronscondensingonthemetalatom.
InFebruary1911,KamerlinOnnis,whomasteredliquidheliumandcryogenictechnology,discoveredthatbelow4.3K,theresistanceofplatinumremainsaconstant,insteadofpassingaminimumvalue.Increase.Therefore,KamerlinOnnisbelievesthattheresistanceofpureplatinumshoulddisappearatthetemperatureofliquidhelium.Inordertoverifythisconjecture,KamerlinOnnischosemercury,whichiseasiertopurify,astheexperimentalobject.First,KamerlinOnniscoolsthemercurytominus40°Ctosolidifythemercuryintoalinearshape;thenusesliquidheliumtoreducethetemperaturetoaround4.2K,andappliesavoltageacrossthemercurywire;whenthetemperatureisslightlylowerthan4.2AtK,theresistanceofmercurysuddenlydisappears,showingasuperconductingstate.
Basiccharacteristics
Superconductorshavethreebasiccharacteristics:completeconductivity,completediamagnetism,andfluxquantization.
Completeconductivity
Completeconductivityisalsocalledzeroresistanceeffect,whichreferstothephenomenonthattheresistancesuddenlydisappearswhenthetemperaturedropsbelowacertaintemperature.
Completeconductivityissuitablefordirectcurrent.Whenthesuperconductorisinanalternatingcurrentoralternatingmagneticfield,therewillbeACloss,andthehigherthefrequency,thegreatertheloss.AClossisanimportantproblemthatneedstobesolvedinthepracticalapplicationofsuperconductors.Atthemacrolevel,theAClossiscausedbythedifferencebetweentheinducedelectricfieldandtheinducedcurrentdensitygeneratedinsidethesuperconductingmaterial;atthemicrolevel,theAClossiscausedbythequantizedmagneticfluxlines.Causedbystagnation.AClossisanimportantparametertocharacterizetheperformanceofsuperconductingmaterials.IftheAClosscanbereduced,thecoolingcostofthesuperconductingdevicecanbereducedandthestabilityoftheoperationcanbeimproved.
Completelydiamagnetic
Meisnereffect(2photos)
Completelydiamagnetic,alsoknownasMeissnereffect,"diamagnetic"Referstothephenomenonthatthemagneticfieldlinescannotpassthroughthesuperconductorwhenthemagneticfieldstrengthislowerthanthecriticalvalue,andtheinternalmagneticfieldofthesuperconductoriszero."Complete"meansthattheorderofthetwooperationsofreducingthetemperaturetothesuperconductingstateandapplyingthemagneticfieldcanbereversed.Thereasonforthecompletediamagnetismisthatthesurfaceofthesuperconductorcanproducealosslessdiamagneticsuperconductingcurrent.Themagneticfieldgeneratedbythiscurrentcancelsthemagneticfieldinsidethesuperconductor.Thezeroresistanceofsuperconductorsiswellknown,butsuperconductorsarenotequivalenttoidealconductors.Startingfromtheelectromagnetictheory,thefollowingconclusionscanbederived:iftheidealconductorisfirstcooledtoalowtemperatureandthenplacedinamagneticfield,theinternalmagneticfieldoftheidealconductoriszero;butiftheidealconductorisplacedinthemagneticfieldfirst,andthencooledtoalowtemperature,theidealThemagneticfieldinsidetheconductorisnotzero.Forsuperconductors,thetwooperationsofloweringthetemperaturetothesuperconductingstateandapplyingthemagneticfield,regardlessoftheirorder,theinternalmagneticfieldofthesuperconductorisalwayszero.Thisisthecoreofcompletediamagnetismandthekeytothedifferencebetweensuperconductorsandidealconductors.
Fluxquantization
FluxquantizationisalsoknownastheJosephsoneffect,whichmeansthatwhentheinsulatinglayerbetweentwosuperconductorsisthintothesizeofanatom,electronpairscanpassthroughtheinsulationThephenomenonthatthelayergeneratestunnelcurrent,thatis,superconductorcurrentcanbegeneratedinthesuperconductor-insulator-superconductorstructure.
TheJosephsoneffectisdividedintotheDCJosephsoneffectandtheACJosephsoneffect.ThedirectcurrentJosephsoneffectmeansthatelectronpairscanformasuperconductingcurrentthroughtheinsulatinglayer.TheACJosephsoneffectmeansthatwhentheappliedDCvoltagereachesacertainlevel,inadditiontotheDCsuperconductingcurrent,thereisalsoACcurrent.Thesuperconductorisplacedinamagneticfieldandthemagneticfieldpenetratestheinsulatinglayer.Themaximumsuperconductingcurrentofthesuperconductingjunctionfollowstheoutside.Thesizeofthemagneticfieldchangesregularly.
Criticalparameters
Superconductorshavethreecriticalparameters:criticaltransitiontemperatureTc,criticalmagneticfieldstrengthHc,criticalCurrentdensityJc.Whenthesuperconductorisinthreecriticalconditionsatthesametime,itshowssuperconductivity.
(1)CriticaltransitiontemperatureTc:WhenthetemperatureislowerthanthecriticaltransitiontemperatureTc,thematerialisinasuperconductingstate;exceedingthecriticaltransitionAttemperatureTc,thesuperconductorreturnsfromthesuperconductingstatetothenormalstate.
(2)CriticalmagneticfieldstrengthHc:WhentheexternalmagneticfieldstrengthexceedsthecriticalmagneticfieldstrengthHc,thesuperconductorisrestoredtothenormalstatefromthesuperconductor.ThecriticalmagneticfieldstrengthHcisrelatedtotemperature,andtherelationshipisasfollows:
(3)CriticalcurrentdensityJc:WhenthecurrentdensitythroughthesuperconductorexceedsthecriticalcurrentdensityJc,thesuperconductorisrestoredtothenormalstatefromthesuperconductor.ThecriticalcurrentdensityJcisrelatedtotemperatureandmagneticfieldstrength.
Theoreticalexplanation
Inordertoclarifythemechanismofsuperconductors,scientistshaveproposedavarietyoftheories,including:theLondonequationthatwasproposedin1935todescribetherelationshipbetweensuperconductingcurrentandweakmagneticfield;Pippardtheoryproposedin1950~1953toperfecttheLondonequation;GL(Ginzburg-Landau)theoryproposedin1950todescribetherelationshipbetweensuperconductingcurrentandstrongmagneticfield(closetothecriticalmagneticfieldstrength);proposedin1957,ExplaintheBCS(Bardeen-Cooper-Schrieffer)theoryofthefirsttypeofsuperconductorfromthemicroscopicmechanism.AmongthemoreimportanttheoriesareBCStheoryandGLtheory.
BCStheory
TheBCStheoryisbasedonthenear-freeelectronmodelandbasedontheweakelectron-phononinteraction.TheproponentsofthetheoryareJ.Bardeen,Cooper,andJ.R.Schrieffer.
TheBCStheorybelievesthatelectronswithoppositespinandmomentuminametalcanpairtoformaCooperpair,andtheCooperpaircanmovewithoutlossinthecrystallatticetoformasuperconductingcurrent.ForthereasonfortheCooperpair,theBCStheoryhasmadethefollowingexplanation:whenelectronsmoveinthelattice,theywillattractthepositivechargesontheneighboringlatticepoints,causinglocaldistortionofthelatticepoints,formingalocalhighpositivechargearea.Thislocalizedhighpositivechargeregionwillattractelectronswithoppositespins,andpairwiththeoriginalelectronswithacertainbindingenergy.Atverylowtemperatures,thisbindingenergymaybehigherthantheenergyofthelatticeatomicvibration,sothattheelectronpairwillnotexchangeenergywiththelattice,andthereisnoresistance,formingasuperconductingcurrent.
TheBCStheoryprovidesagoodmicroscopicexplanationofthereasonsfortheexistenceofthefirsttypeofsuperconductors,andtheproponentsofthetheoryBarding,Cooper,andSchrieverwontheNobelPrizeinPhysicsin1972.However,theBCStheorycannotexplaintheexistenceofthesecondtypeofsuperconductor,especiallytheMcMillanlimittemperature(thecriticaltransitiontemperatureofasuperconductorcannotbehigherthan40K)basedontheBCStheory,whichhaslongbeenbrokenbythesecondtypeofsuperconductor.
GLtheory
GLtheoryisaphenomenologicaltheoryproposedonthebasisofLandau'ssecond-orderphasetransitiontheory.TheproponentsofthetheoryareGinzburgandLandau.
TheGLtheoryisbasedonthefollowingconsiderations:whentheexternalmagneticfieldstrengthisclosetothesuperconductor'snearbymagneticfieldstrength,thesuperconductor'scurrentdoesnotobeythelinearlaw,andthezero-pointvibrationenergyofthesuperconductorcannotbeignored.
ThegreatestcontributionofGLtheoryistoforeseetheexistenceofthesecondtypeofsuperconductor.StartingfromtheGLtheory,theconceptofsurfaceenergyκcanbederived.Whenthesurfaceenergyofthesuperconductorisκ,itisthefirsttypeofsuperconductor;whenthesurfaceenergyofthesuperconductorisκ,itisthesecondtypeofsuperconductor.
Classification
Theclassificationmethodsofsuperconductorsareasfollows:
(1)Accordingtotheresponseofthematerialtothemagneticfield:thefirsttypeofsuperconductorandthesecondtypeofsuperconductor.Fromtheperspectiveofmacro-physicalproperties,thefirsttypeofsuperconductorhasonlyasinglecriticalmagneticfieldstrength;thesecondtypeofsuperconductorhastwocriticalmagneticfieldstrengthvalues.Betweenthetwocriticalvalues,thematerialallowspartofthemagneticfieldtopenetratethematerial.Fromatheoreticalpointofview,asstatedintheGLtheoryinthe"TheoreticalExplanation"above,theparameterκisthecriterionfordividingtwotypesofsuperconductors.
Amongtheelementalsuperconductorsthathavebeendiscovered,thefirsttypeofsuperconductoraccountsforthemajority,andonlyvanadium,niobium,andtechnetiumbelongtothesecondtypeofsuperconductor;however,manyalloysuperconductorsandcompoundsuperconductorsbelongtothesecondtypeofsuperconductor.
(2)Accordingtotheinterpretationtheory:traditionalsuperconductors(canbeexplainedbyBCStheoryoritsinferences)andnon-traditionalsuperconductors(cannotbeexplainedbyBCStheory).
(3)Accordingtothecriticaltemperature:hightemperaturesuperconductorandlowtemperaturesuperconductor.High-temperaturesuperconductorsusuallyrefertosuperconductorswhosecriticaltemperatureishigherthanthetemperatureofliquidnitrogen(greaterthan77K),andlow-temperaturesuperconductorsusuallyrefertosuperconductorswhosecriticaltemperatureislowerthanthetemperatureofliquidnitrogen(lessthan77K).
(4)Accordingtothetypeofmaterial:elementalsuperconductors(suchasleadandmercury),alloysuperconductors(suchasniobium-titaniumalloy),oxidesuperconductors(suchasyttriumbariumcopperoxide),organicsuperconductors(suchascarbonnanoTube).
Historyofdevelopment
Mid-early20thcentury
In1911,theDutchscientistKamelin-Onnesusedliquidheliumtocoolmercury.Whenthetemperaturedroppedto4.2AtK(-268.95°C),theresistanceofmercurycompletelydisappears,andKamerincallsthisphenomenonsuperconductivity.KamerlinwontheNobelPrizein1913forthis.
In1933,MeissnerandOxenfeldscientistsdiscoveredthecompletediamagnetismofsuperconductors,whichlatercametocallthe"Meisnereffect."
FromMarch16,1954toSeptember5,1956,inordertoverifythattheresistanceofthesuperconductorwaszero,scientistsputaleadringwithatemperaturelowerthanTc=7.2Kspace,usingelectromagneticinductiontoexciteaninducedcurrentinthering.Thecurrenthasnotdecayedfortwoandahalfyears,whichshowsthatthereisnolossofelectricenergyinthering.WhenthetemperaturerisesaboveTc,theringchangesfromasuperconductingstatetoanormalstate.Theresistanceofthematerialincreasessuddenly,andtheinducedcurrentdisappearsimmediately.ThisisthefamousOnnissPersistentCurrentExperiment.
In1962,Josephson,agraduatestudentattheUniversityofCambridge,theoreticallypredictedthatelectronscouldpassthroughthethininsulatinglayerbetweentwosuperconductors.Inlessthanayear,AndersonandRowelletal.TheaboveconfirmedJosephson’sprophecy.Thisimportantdiscoveryprovidesevidenceforthemovementofelectronpairsinsuperconductors,anddeepenstheunderstandingofthenatureofsuperconductivity.TheJosephsoneffectbecamethebasisforthedetectionofweakelectromagneticsignalsandotherelectronicapplications.
Inthe1970s
In1973,asuperconductingalloy,niobium-germaniumalloy,wasdiscovered.Itscriticalsuperconductingtemperaturewas23.2K(﹣249.95℃).Thisrecordhasbeenmaintained.Nearly13years.
In1979,thesuperconductingtrainsuccessfullycarriedoutamannedfeasibilitytestontheMiyazakiLine,Japan’stestrailway,withaspeedof517kilometersperhour.
1980s
In1980,BechgaardandothersinDenmarksynthesizedthefirstorganicsuperconductor(TMTSF)2PF6.
In1986,MullerandBenozdiscoveredthataceramicmetaloxidecomposedofbarium,lanthanum,copper,andoxygen,LaBaCuO4,hashightemperaturesuperconductivityandcriticalThetemperaturecanreach35K(﹣240.15℃).Sinceceramicmetaloxidesareusuallyinsulatingmaterials,thisdiscoveryisofgreatsignificance,andMuellerandBenozwontheNobelPrizeinPhysicsin1987.Sincethen,researchonhigh-temperaturesuperconductivityhasdevelopedrapidly.
In1986,BellLaboratoriesoftheUnitedStatesdevelopedasuperconductingmaterialwithacriticalsuperconductingtemperatureof40K(-235.15℃),breakingthe"temperaturebarrier"(40K)ofliquidhydrogen.
In1987,ChineseAmericanscientist,UniversityofHoustonprofessorZhuJingwu,andChinesescientistZhaoZhongxiansuccessivelydevelopedyttrium-barium-copper-oxygenmaterials.Thecriticalsuperconductingtemperaturewasincreasedto90K(﹣185.15℃)above,breakingThe"temperaturebarrier"ofliquidnitrogen(77K).
Attheendof1987,itwasdiscoveredthatthecriticaltemperatureofthethallium-barium-calcium-copper-oxygensystemreached125K(-150.15°C).Injustoverayearfrom1986to1987,thecriticalsuperconductingtemperaturehasincreasedbynearly100K.
In1988,Hitachi,Ltd.ofJapandiscoveredthatthecriticaltemperatureofmercury-basedsuperconductingmaterialsreached135K.Underhighpressureconditions,thecriticaltemperaturecouldreach164K.
90softhe20thcentury
InMarch1991,SumitomoElectricIndustriesofJapandemonstratedtheworld'sfirstsuperconductingmagnet.
InOctober1991,JapanAtomicEnergyResearchInstituteandToshibaCorporationjointlydevelopedasuperconductingcoilfornuclearfusionreactorsmadeofniobiumandtincompounds.Thecurrentdensityofthecoilreaches40amperespersquaremillimeter,whichismorethanthreetimesthatofthepast.
In1992,asuperconductingsupercolliderbasedongiantsuperconductingmagnetswasbuiltandputintouseinTexas,USA,atacostofmorethan8.2billionU.S.dollars.
OnJanuary27,1992,builtbytheJapanShipandOceanFoundation,thefirstshipwithsuperconductingmagneticfluidpropulsion,the"Yamato"No.1,waslaunchedinKobe,Japanforseatrials.
In1996,EuropeancablegiantPirelliCableCompany,AmericanSuperconductorCompanyandSanFranciscoElectricPowerResearchInstitutejointlyproducedthefirstundergroundhigh-temperaturesuperconductingpowertransmissioncable.Thecableis6000meterslongandiswoundwithbismuth-Strontium-calcium-copper-oxygensuperconductingmaterialmadeofliquidnitrogenemptytube.
In1999,BernhardandothersoftheGermanPlanckInstitutediscoveredthattherutheniumcoppercompoundRuSr2GdCu2O8-δIthasbothsuperconductivityandferromagneticorder.Itssuperconductingcriticaltemperatureis15-40Kandferromagnetictransitiontemperatureis133-136K.Becausethecompoundhasbothsuperconductivityandferromagneticorder,ithasgreatapplicationpotentialincomputerdatastorage.
Thebeginningofthe21stcentury
OnJanuary29,2004,ajointresearchteamcomposedofscientistsfromtheAmericanInstituteofStandardsandTechnologyandtheUniversityofColoradoproposedanewformofmatter-feeYonagocondensate(fermioniccondensate),andpredictsthatitwillhelphumansmakethenextgenerationofsuperconductors.
In2006,ProfessorHideoHosonoofTokyoInstituteofTechnology,Japan,synthesizedLaFeOP,acompoundwithironasthemainbodyofsuperconducting,andpioneeredthestudyofiron-basedsuperconductors.
InSeptember2012,theUniversityofLeipziginGermanydiscoveredthatgraphiteparticlescanexhibitsuperconductivityatroomtemperature.
Researchtrends
Copper-oxygensuperconductors
Copper-oxygensuperconductorsarethefirsthigh-temperaturesuperconductorsdiscovered.ThebariumsynthesizedbyMullerandBenozinthe1980sThelanthanum-copper-oxygenserieshigh-temperaturesuperconductorsandtheyttrium-barium-copper-oxygenserieshigh-temperaturesuperconductorssynthesizedbyZhuJingwuandZhaoZhongxianallbelongtothiscategory.
Copper-oxygensuperconductorsinclude90Krareearthseries,110Kbismuthseries,125Kthalliumseries,and135Kmercuryseriessuperconductors.Theyallcontaincopperandoxygen,sotheyarecalledcopper-oxygensuperconductors.Thecopper-oxygensuperconductorhasasimilarlayeredcrystallinestructure,inwhichthecopper-oxygenlayerisasuperconductinglayer.
Theresearchoncopper-oxygensuperconductorspresentsthefollowingtrends:First,copper-oxygensuperconductorsarerelativelymature.Forexample,devicesmadeofthallium-barium-calcium-copper-oxygensuperconductingfilmshavebeenusedinmobilephones.Transmissiontowertoincreasecapacityandreducedisconnectionandexternalinterference.Secondly,thebasicresearchofcopper-oxygensuperconductorsisatabottleneckstage,andthetransitiontemperaturehasnotbeenabletoexceed164K.Third,theresearchonthemechanismofcopper-oxygensuperconductorshasmadeprogress.Forexample,in2002,scientistsinGermany,France,andRussiausedneutronscatteringtechnologytocreateasinglecopper-oxygenlayerTl2Ba2CuO6+δobservedmagneticresonance,whichishelpfultotheinvestigationofthemechanismofcopperoxidesuperconductors.
Iron-basedsuperconductors
Sincethediscoveryofiron-basedsuperconductorsin2006,therehasbeenadeepeningofiron-basedsuperconductors.Themoreprominentresultsare:In2008,JapanesescientistHideoHononodiscovereddopingF’sLaFeOPsuperconductorhasacriticaltemperatureof26K;in2008,ChinesescientistsZhaoZhongxian,ChenXianhui,WangNanlin,WenHaihu,andFangZhongdiscoveredSmFeAs1-xFxwithacriticaltemperatureof43K.SuperconductorsandReFeAs1-xFxsuperconductorswithacriticaltemperatureof55KbrokethroughtheMcMillanlimittemperatureof40Kforthefirsttimeinthefieldofiron-basedsuperconductors.
Iron-basedsuperconductorshaveattractedattentionfortworeasons:First,Feionsaremagneticions,whichbreakstheviewthatmagneticionsarenotconducivetosuperconductivity,andprovidesawaytoexplorenewsuperconductors.;Second,similartocopper-oxygensuperconductors,iron-basedsuperconductorsalsohavestrongelectron-spininteractions,whichareofreferencevalueforprobingthemechanismofhigh-temperaturesuperconductivity.
MagnesiumBorideSuperconductor
InJanuary2001,ProfessorJ.AkimitsufromAoyamaGakuinUniversityinJapanandothersdiscoveredforthefirsttimethatMgB2hassuperconductivity.Thecriticaltemperatureisabout39K.
AlthoughMgB2hasalowercriticaltemperature,itstillhasmanyadvantagescomparedwithcopper-oxygensuperconductorsandiron-basedsuperconductors,including:simplestructureandeasypreparation;sourceofrawmaterialsWiderange,lowcost;easytoprocess.Inparticular,theeaseofprocessinghasbecomeanimportantadvantageofMgB2.Becausethecopper-oxygensuperconductorwithhighcriticaltemperatureisessentiallyaceramicmaterial,thehardnessoftheceramicmaterialislargeandtheprocessingisdifficult,whichhasbecomeafactorrestrictingthedevelopmentofthecopper-oxygensuperconductor.MgB2superconductorscanmakeupforthisdeficiency.
Applications
Theapplicationsofsuperconductorscanbedividedintothreecategories:strongcurrentapplications,weakcurrentapplicationsanddiamagneticapplications.Strongcurrentapplicationsarehighcurrentapplications,includingsuperconductingpowergeneration,powertransmissionandenergystorage;weakcurrentapplicationsareelectronicsapplications,includingsuperconductingcomputers,superconductingantennas,superconductingmicrowavedevices,etc.;diamagneticapplicationsmainlyincludemaglevtrainsandthermonucleiFusionreactor,etc.
Strongcurrentapplication
Superconductinggenerator:Superconductinggeneratorhastwomeanings.Onemeaningistoreplacethecopperwindingsofordinarygeneratorswithsuperconductorwindingstoimprovecurrentdensityandmagneticfieldstrength.Ithastheadvantagesoflargegeneratingcapacity,smallsize,lightweight,smallreactanceandhighefficiency.Anothermeaningreferstothesuperconductingmagneticfluidgenerator.Themagneticfluidgeneratorhastheadvantagesofhighefficiencyandlargepowergenerationcapacity.However,thetraditionalmagnetwillproducealotoflossduringthepowergenerationprocess,whilethesuperconductingmagnetitselfhaslowlossandcanbeMakeupforthisshortcoming.
Superconductingpowertransmission:Superconductingwiresandsuperconductingtransformersmadeofsuperconductingmaterialscantransmitelectricitytousersalmostwithoutloss.Accordingtostatistics,about15%oftheelectricityislostonthetransmissionlinewithcopperoraluminumwires.InChinaalone,theannualelectricitylossismorethan100billionkWh.Ifitischangedtosuperconductingpowertransmission,theenergysavedisequivalenttotheconstructionofdozensoflarge-scalepowerplants.
Lightcurrentapplications
Superconductingcomputers:High-speedcomputersrequiredenselyarrangedcomponentsandconnectinglinesonintegratedcircuitchips,butdenselyarrangedcircuitswillgeneratealotofheatduringoperation,andHeatdissipationisaproblemfacedbyVLSI.Theverylargescaleintegratedcircuitinthesuperconductingcomputer,theinterconnectionlinebetweenitscomponentsismadeofsuperconductingdeviceswithclosetozeroresistanceandultra-microheating,thereisnoheatdissipationproblem,andthecomputingspeedofthecomputerisgreatlyimproved.Inaddition,scientistsarestudyingtheuseofsemiconductorsandsuperconductorstomaketransistors,andevencompletelyusesuperconductorstomaketransistors.
Diamagneticapplications
Superconductingmagneticlevitationtrain:Usingthediamagnetismofsuperconductingmaterials,placethesuperconductingmaterialontopofapermanentmagnet,becausethemagneticfieldlinesofthemagnetcannotpassthroughthesuperconductor,Therewillbearepulsiveforcebetweenthemagnetandthesuperconductor,causingthesuperconductortofloatabovethemagnet.Thiskindofmagneticlevitationeffectcanbeusedtomakehigh-speedsuperconductingmagneticlevitationtrains.
Nuclearfusionreactor"magneticenclosure":Duringthenuclearfusionreaction,theinternaltemperatureisashighas100to200milliondegreesCelsius,andthereisnoconventionalmaterialthatcancontainthesesubstances.Thestrongmagneticfieldgeneratedbythesuperconductorcanbeusedasa"magneticenclosure"toencloseandconfinetheultra-hightemperatureplasmainthethermonuclearreactor,andthenslowlyreleaseit,therebymakingcontrollednuclearfusionenergyapromisingnewenergysourceinthe21stcentury.
Criticaltemperature
Criticaltemperatureofsuperconductingmaterials
Materials | Symbols | Tc(K) | NumberofCu-Oplanesintheunitcell | Structure |
|---|---|---|---|---|
YBa2Cu3O7 | 123 | 92 | 2 | orthogonalsystem |
Bi2Sr2CuO6 | Bi-2201 | 20 | 1 | Tetragonalcrystalsystem |
Bi2Sr2CaCu2O8 | Bi-2212 | 85 | 2 | Tetragonalcrystalsystem |
Bi2Sr2Ca2Cu3O6 | Bi-2223 | 110 | 3 | Tetragonalcrystalsystem |
Tl2Ba2CuO6 | Tl-2201 | 80 | 1 | Tetragonalcrystalsystem |
Tl2Ba2CaCu2O8 | Tl-2212 | 108 | 2 | tetragonalcrystalsystem |
Tl2Ba2Ca2Cu3O10 | Tl-2223 | 125 | 3 | Tetragonalcrystalsystem |
TlBa2Ca3Cu4O11 | Tl-1234 | 122 | 4 | tetragonalcrystalsystem |
HgBa2CuO4 | Hg-1201 | 94 | 1 | tetragonalcrystalsystem |
HgBa2CaCu2O6 | Hg-1212 | 128 | 2 | Tetragonalcrystalsystem |
HgBa2Ca2Cu3O8 | Hg-1223 | 134 | 3 | Tetragonalcrystalsystem |
Theoreticalprogress
AmericanphysicistsJohnBarding,LeonCooper,andJohnSchrieverputforwardtheBCStheoryandpointedoutthekeyroleofelectro-acousticcoupling,whichexplainedthelow-temperaturesuperconductivitymoresatisfactorily.Theoreticalresearchonhigh-temperaturesuperconductivityisstillinprogress.
InSeptember2012,researchersattheUniversityofLeipziginGermanyannouncedaprogress:graphiteparticlescanexhibitsuperconductivityatroomtemperature.Theresearchersimmersedthegraphitepowderinwater,filtereditout,andplaceditinamagneticfield.Asaresult,asmallportion(approximately0.01%)ofthesamplesshoweddiamagnetism,anddiamagnetismisoneofthehallmarkcharacteristicsofsuperconductingmaterials.Althoughtherearefewgraphiteparticlesexhibitingsuperconductivity,thisdiscoveryisstillofgreatsignificance.Sofar,superconductorscanonlyfunctionattemperaturesbelow-70°C.Ifacheapandeasilyavailablemateriallikegraphitepowdercanreallyachievesuperconductivityatroomtemperature,itwilltriggeranewmodernindustrialrevolution.
Purpose
SuperconductingmagnetscanbeusedtomakeACsuperconductinggenerators,magneticfluidgeneratorsandsuperconductingtransmissionlines.Thesuperconductingquantuminterferometer(SQUID)hasbeenindustrialized.Inaddition,NbTialloyandNb3Sn,whicharethemainrepresentativesoflow-temperaturesuperconductingmaterials,aremainlyusedinMRI(magneticresonanceimaging)inthemedicalfieldinthecommercialfield.Asascientificresearchfield,ithasbeenappliedtothelarge-scaleEuropeanprojectLHCprojecttohelphumansseekscientificissuessuchastheoriginoftheuniverse.
Generatingamagneticfield
Whenaconventionalconductorisusedasamagnet,itneedstogenerateasteady-statestrongmagneticfieldofmorethan100,000Gauss,whichrequires3.5megawattsofelectricpowerandalargeamountofTheinvestmentincoolingwaterishuge;andthesuperconductingmaterialhaszeroresistanceanddiamagnetisminthesuperconductingstate,soitonlyneedstoconsumeverylittleelectricenergytoobtainsuchalargesteady-statestrongmagneticfield.