We study the Fermi surface of Bi2Sr2CaCu2O8 (Bi2212) using angle resolved photoemission (ARPES) with a momentum resolution of ~ 0.01 of the Brillouin zone. We show that, contrary to recent suggestions, the Fermi surface is a large hole barrel centered at (

TheFermisurfaceofBi2Sr2CaCu2O8

H.M.Fretwell,1 A.Kaminski,1,2J.Mesot,2 J.C.Campuzano,1,2M.R.Norman,2M.Randeria,3T.Sato,4R.

Gatt,1T.Takahashi,4andK.Kadowaki5

arXiv:cond-mat/9910221v1 [cond-mat.supr-con] 14 Oct 1999

(1)DepartmentofPhysics,UniversityofIllinoisatChicago,Chicago,IL60607(2)MaterialsSciencesDivision,ArgonneNationalLaboratory,Argonne,IL60439

(3)TataInstituteofFundamentalResearch,Mumbai400005,India(4)DepartmentofPhysics,TohokuUniversity,980-8578Sendai,Japan(5)InstituteofMaterialsScience,UniversityofTsukuba,Ibaraki305,Japan

WestudytheFermisurfaceofBi2Sr2CaCu2O8(Bi2212)usingangleresolvedphotoemission(ARPES)withamomentumresolutionof～0.01oftheBrillouinzone.Weshowthat,contrarytorecentsuggestions,theFermisurfaceisalargeholebarrelcenteredat(π,π),independentoftheincidentphotonenergy.PACSnumbers:71.25.Hc,74.25.Jb,74.72.Hs,79.60.Bm

TheFermisurface,thelocusinmomentumspaceofgaplesselectronicexcitations,isacentralconceptinthetheoryofmetals.Despitethefactthattheopti-mallydopedhightemperaturesuperconductorsdisplayananomalousnormalstatewithnowell-de nedquasi-particles[1],manyangleresolvedphotoemissionspec-troscopy(ARPES)studiesusingphotonenergiesintherangeof19-22eVhaveconsistentlyrevealedalargehole-likeFermisurfacecenteredat(π,π)[2–5]withavolumeconsistentwiththeLuttingercountof(1 x)electrons(wherexistheholedoping).Thiswidelyacceptedpic-turehasrecentlybeenchallengedbytwostudies[6,7]whichsuggestadi erentFermisurfacewhenmeasuredatahigherphotonenergy(32-33eV).Theserecentstud-iesproposethattheFermisurfaceconsistsofalargeelec-tronpocketcenteredon(0,0)withaclearviolationoftheLuttingercount.Toreconciletheirmodelwithpreviousdataat22eVphotonenergy,theseauthorssuggestthepresenceof“additionalstates”near(π,0),possiblyduetostripeformation.SettingasideforthemomenttheimportantquestionofwhatthetrueFermisurfaceofBi2212is,theimplicationofaphotonenergydependentFermisurfacefromARPESdataisparticularlyworri-some,anddeservestobeaddressed.

Here,wepresentextensiveARPESdatatakenatvar-iousphotonenergiesand ndclearevidencethattheFermisurfacemeasuredbyARPESisindependentofphotonenergy,andconsistsofasingleholebarrelcen-teredat(π,π).AlthoughthedataofRefs.arecon-sistentwithours,theirlimitedsamplingoftheBrillouinzoneandlowermomentumresolutionleadtoamisin-terpretationofthetopologyoftheFermisurface.ThisoccursbecauseofthepresenceofghostimagesoftheFermisurfaceduetodi ractionoftheoutgoingphoto-electronsbyaQvectorof±(0.21π,0.21π)associatedwiththesuperlatticemodulationintheBiOlayers(umklappbands).Inparticular,infollowingaFermicontour,ifthedataarenotdenseenoughink-space,ornotofsu -cientlyhighmomentumresolution,onecaninadvertently“jump”fromthemainbandtooneoftheumklappbands,concludingincorrectlythatthetopologyoftheFermisurfaceiselectron-like.Thisisparticularlyrelevantatthephotonenergyof33eVbecauseofastrongsuppres-sionoftheARPESmatrixelementsatkpointsinthevicinityof(π,0),a nalstatee ect,resultinginalargeumklapp/mainbandsignalrationear(0.8π,0)wherethepurportedelectronFermisurfacecrossingoccurs.

ARPESprobestheoccupiedpartoftheelectronspec-trum,andforquasi-2DsystemsitsintensityI(k,ω)isproportionaltothesquareofthedipolematrixelement,theFermifunctionf(ω),andtheone-electronspectralfunctionA(k,ω)[8].Themeasuredenergydistributioncurve(EDC)isobtainedbytheconvolutionofthisinten-sitywithexperimentalresolution.Inanotherpaper,wediscussingreatdetailthevariousmethodologiesforde-terminingtheFermisurfacefromARPESdataHere,welookattwoquantities:(1)thedispersionofspectralpeaksobtainedfromtheenergydistributioncurves,and(2)theARPESintensityintegratedoveranarrowenergyrangeabouttheFermienergyAswewillshow,thesemethodsmustbetreatedwithcarebecauseofthekde-pendenceofthematrixelementsandthepresenceoftheumklappbands.

TheARPESexperimentswereperformedattheSyn-chrotronRadiationCenter,Wisconsin,usingaplanegratingmonochromatorbeamlinewitharesolvingpowerof104at1012photons/s,combinedwithaSCIENTA-200electronanalyserusedinangleresolvedmode.Atypicalmeasurementinvolvedthesimultaneouscollec-tionandenergy/momentumdiscriminationofelectronsovera～12 range(cut)withanangularresolutionwin-dowof～(0.5 ,0.26 )(0.26 paralleltothecut).Thiscorrespondstoamomentumresolutionof(0.038,0.020)π,(0.029,0.015)π,and(0.022,0.012)πat55,33,and22eVrespectively.Theenergyresolutionforalldatawas～16meV(FWHM).

Thequalityoftheoptimallydopedsinglecrystalsam-plescannotbeemphasizedenough,particularlyinre-