Photoemission Spectroscopy on High Temperature Superconductor: A Study of Bi2Sr2CaCu2O8 by Laser-Based Angle-Resolved Photoemission

146 Pages·2013·6.64 MB·English

by  Wentao Zhang (auth.)

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Wentao Zhang
Photoemission
Spectroscopy on
High Temperature
Superconductor
A Study of Bi Sr CaCu O by Laser-Based
2 2 2 8
Angle-Resolved Photoemission
Author Supervisor
Dr.WentaoZhang Prof.XingjiangZhou
LawrenceBerkeleyNationalLaboratory InstituteofPhysics
Berkeley,CA ChineseAcademyofSciences
USA Beijing,China
ISSN2190-5053 ISSN2190-5061(electronic)
SpringerTheses
ISBN978-3-642-32471-0 ISBN978-3-642-32472-7(eBook)
DOI10.1007/978-3-642-32472-7
SpringerHeidelbergNewYorkDordrechtLondon
LibraryofCongressControlNumber:2012946742
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Supervisor’s Foreword
The properties of solid materials are dictated by their inherent electronic struc-
tureswhichincludethreebasicphysicalparameters,energy(E),momentum(k)and
spin (s) of electrons. Angle-resolved photoemission spectroscopy (ARPES), with
additional spin detections, as a powerful tool in probing these basic parameters
in materials, has been widely used in the condensed matter physics. Distinguish-
ing from the previous ARPES studies, this book mainly focuses on the study of
high-temperaturesuperconductorBi Sr CaCu O bysuper-highresolutionARPES
2 2 2 8
equippedwithavacuumultra-violet(VUV)laser,focusedonthemany-bodyeffects
(Chaps.4and5),electron-holemixture(Chap.6),superconductinggap,andpseu-
dogap(Chap.7).
The mechanism of high temperature superconductivity in copper-oxide com-
pounds(cuprates)remainsunclearafteritsfirstdiscoveryin1986.Manyadvanced
experimental techniques have been applied on these materials, and great progress
hasbeenmadeinunderstandingrelatedphysicsandsuperconductivity.Amongthese
progressesare:thed-wavepairingsymmetryidentifiedbyphasesensitivetechnique
tunneljunctions,aswellasbyARPESandothertechniques,theuniversalelectron-
boson coupling revealed by ARPES, antiferromagnetic correlations or spin reso-
nancediscoveredbyneutronscattering,thecomplicatedphasediagramstudiedby
various doping dependent experiments, the complex energy gap structure and the
pseudogap above transition temperature, the unusual oxygen isotope effect and so
on. In these discoveries, many of them were studied by ARPES which is a tech-
niquethatprobesthefundamentalsingleparticlespectralfunctioninmaterials.The
currentstatusofthestudyofcupratesuperconductorsisintroducedinChap.1.
TheARPEStechniquehasseencontinuousdevelopmentwithtime.Thedistinct
difference of the ARPES technique in this book is a high resolution spectroscopy
system combined with a narrow band vacuum ultra-violet (VUV) laser, giving a
total energy resolution better than 1 meV which has been greatly improved from
the previous spectroscopy systems equipped with synchrotron light source or gas
dischargelamp.InChap.2,basedontheVUVlaser,developmentofanewgener-
ation ARPES, another spin-resolve ARPES, and ARPES system based on a latest
time-of-flightelectronenergyanalyzerareintroduced.
v
vi Supervisor’sForeword
Because of its easiness to cleave to provide a smooth, clean and neutral sur-
face,Bi Sr CaCu O isoneofthemostpopularlystudiedcupratesuperconductors
2 2 2 8
by ARPES. Because cleaving process destroys samples, large amount s of sam-
ples is needed in the ARPES study of cuprate high-temperature superconductiv-
ity. In order to cover the complex electronic phase diagram, single crystals with a
widedopingrangearealsonecessary.Chapter3describesthegrowthofhighqual-
ity Bi2Sr2CaxDy1−xCu2O8 single crystals from heavily underdopingto optimally
doping.Alsointroducedinthischapteristheprocessofobtainingoverdopedsingle
crystalsbyannealingmethod.
InChap.4,theidentificationofanewformofelectroncouplinginBi2212from
thenodaldispersionispresented.Inadditiontoenergyscalesknownfromprevious
ARPES measurements, new features at energy ∼115 meV and ∼150 meV were
identified by ultra-high resolution VUV Laser-based ARPES. Moreover, detailed
temperaturedependenceofnodalelectronicdynamicsindicatesastrongsensitivity
ofthenodalstatetohightemperaturesuperconductivity.
Chapter5 describes the study on the nature of high energy dispersion and high
energykinkinBi2212.Bydetailedmomentumdependenceexperiments,combined
with MDC (momentum distribution curve) and EDC (energy distribution curve)
analyses,ithasbeenproposedthatthehighenergyMDCdispersion(upto∼1eV)
does not represent true bare band, the high energy “kink” (∼400 meV) does not
representelectroncouplingwithsomehighenergymodesandthehighenergyMDC
dispersionmaynotrepresentintrinsicbandstructure.
Chapter 6 demonstrates the direct observation of the electron-hole mixing in
Bi2212atlow temperature.By fittingthemomentumdistributioncurves(MDCs),
thecomplexelectronself-energyandcomplexgapfunctioninsuperconductingstate
were extracted. The obtained complex gap function could be used to extract the
bosonicspectralfunctionassociatedwithhigh-temperaturesuperconductivity.
Chapter7presentsthestudyofthesuperconductingenergygapandthepseudo-
gapinnormalstate.Thehigh-precisionARPESmeasurementsonmomentumand
temperaturedependenceofenergygapindicatesthatsimple“twogap”or“onegap”
scenarioscannotgiveagooddescriptionoftheresults.
Wehopetheexperimentalmethodsandscientificresults presentedinthisbook
willshedsomeinsightsinthestudyofhigh-temperaturesuperconductors.Wewould
liketonotethatofsuchsuper-highresolutionARPESexperimentsoncupratesuper-
conductorsarestillinprogressandmanynewresultsarecoming.WethankSpringer
for their encouragement, and thank the staff of Springer for their support and pa-
tience.
InstituteofPhysics Prof.Dr.XingjiangZhou
ChineseAcademyofSciences
Beijing
Acknowledgement
FirstIwouldliketosincerelythankmysupervisorProf.XingjiangZhou,whohas
alwayssupportedme.Hisrigorousattitudetowardscholarshipandthepursuitofex-
cellencearesomethingIfeelhaveshapedmywholelife.AlltheknowledgeIgained
inhisgroupandthecompletionofthisthesiswereunderhispersonalguidance.He
provideduswitharelaxedandvibrantresearchenvironmentthatgaveusthefree-
domtounfoldourownimaginationandcreativity.Hewasapproachable,andnever
blamed us for mistakes we made. He is not only the perfect supervisor, but also a
goodfriend.
I’m also very grateful to Guodong Liu, Xiaoli Dong, Jun Zhang and Shaolong
He, who gave me many helpful and valuable suggestions for my research at the
InstituteofPhysics.
GreatthanksgotoProf.ZhongxianZhao,whohadtheforesighttosuggestthatI
jointheZhougroup.IreallyenjoyedtheresearchandtheinvaluabletimeIspentin
thisgroup.
ManythankstoLinZhaoandHaiyunLiuwhoworkedhard,dayandnight,with
meinthelab.Ihavereallyenjoyedworkingwiththem.ThankstoJunfengHe,who
spentconsiderabletimeperfectingmythesis.
Thanks to my parents, my brother, his wife and his two lovely sons. Thanks to
theirsupport,Iwasabletoconcentrateonmyinterestinresearch.
Andlastly,manythankstomywife,ShanyuLiuandherparents.Iwillcherish
hercaring,wisdomandunderstandingmywholelifelong.
vii
Parts of This Thesis Have Been Published
in the Following Journal Articles
WentaoZhang,Junfeng He,GuodongLiu, LinZhao,HaiyunLiu, JianqiaoMeng,
Xiaowen Jia, Yingying Peng, Daixiang Mou, Shanyu Liu, Li Yu, Shaolong He,
Xiaoli Dong, Jun Zhang and X.J. Zhou, Extraction of normal electron self-energy
and pairing self-energy in the superconducting state of the Bi Sr CaCu O su-
2 2 2 8
perconductor via laser-based angle-resolved photoemission, Phys. Rev. B 85,
064514(2012).
Wentao Zhang, Guodong Liu, Jianqiao Meng, Lin Zhao, Haiyun Liu, Xiaoli
Dong,WeiLu,J.S.Wen,Z.J.Xu,G.D.Gu,T.Sasagawa,GuilingWang,YongZhu,
Hongbo Zhang,Yong Zhou, Xiaoyang Wang, Zhongxian Zhao, Chuangtian Chen,
ZuyanXuandX.J.Zhou,HighenergydispersionsinBi Sr CaCu O hightemper-
2 2 2 8
aturesuperconductorbylaser-basedangle-resolvedphotoemission,Phys.Rev.Lett.
101,017002(2008).
Wentao Zhang, Guodong Liu, Lin Zhao, Haiyun Liu, Jianqiao Meng, Xiaoli
Dong, Wei Lu, J.S. Wen, Z.J. Xu, G.D. Gu, T. Sasagawa, Guiling Wang, Yong
Zhu, Hongbo Zhang,Yong Zhou, Xiaoyang Wang, Zhongxian Zhao, Chuangtian
Chen, Zuyan Xu and X.J. Zhou, Identification of a new form of electron coupling
in Bi Sr CaCu O superconductor by laser-based angle-resolved photoemission,
2 2 2 8
Phys.Rev.Lett.100,107002(2008).
Guodong Liu, Guiling Wang, Yong Zhu, Hongbo Zhang, Guochun Zhang, Xi-
aoyang Wang, Yong Zhou,Wentao Zhang, Haiyun Liu, Lin Zhao, Jianqiao Meng,
Xiaoli Dong, Chuangtian Chen, Zuyan Xu and X.J. Zhou, Development of a vac-
uumultra-violetlaser-basedangle-resolvedphotoemissionsystemwithasuper-high
energy resolution better than 1 meV, Review of Scientific Instruments 79, 023105
(2008).
ix
Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1 HistoryofSuperconductivity . . . . . . . . . . . . . . . . . . . . 1
1.2 IntroductiontoCuprates . . . . . . . . . . . . . . . . . . . . . . . 4
1.2.1 TheCrystalStructureofCuprates . . . . . . . . . . . . . . 4
1.2.2 ThePhaseDiagramofCuprates . . . . . . . . . . . . . . . 5
1.2.3 ElectronicStructureofCuprates[27] . . . . . . . . . . . . 7
1.2.4 SummarytotheStudyofCuprateSuperconductors. . . . . 9
1.3 ARPESStudyonCuprateSuperconductors . . . . . . . . . . . . . 9
1.3.1 TheFermiSurfaceofBi2212 . . . . . . . . . . . . . . . . 10
1.3.2 ARPES Study on the Many-Body Effect of Cuprate
Superconductors . . . . . . . . . . . . . . . . . . . . . . . 10
1.3.3 SuperconductingGapandPseudogapbyARPES . . . . . . 12
1.3.4 Summary to the Study of Cuprate Superconductors
byARPES . . . . . . . . . . . . . . . . . . . . . . . . . . 13
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2 Angle-ResolvedPhotoemissionSpectroscopy. . . . . . . . . . . . . . 19
2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.2 ThePrincipleofARPES[3] . . . . . . . . . . . . . . . . . . . . . 19
2.2.1 BriefDescriptionofARPES. . . . . . . . . . . . . . . . . 20
2.2.2 SingleParticleSpectralFunction . . . . . . . . . . . . . . 22
2.3 Ultra-VioletLaser-BasedARPES . . . . . . . . . . . . . . . . . . 23
2.3.1 VUVLaserLightSource . . . . . . . . . . . . . . . . . . 25
2.3.2 SpectroscopySystem . . . . . . . . . . . . . . . . . . . . 28
2.3.3 PerformanceoftheSystem[2] . . . . . . . . . . . . . . . 32
2.4 The Developmentof Spin-ResolvedARPES, Time-of-Flight
ARPESandTunableLaserARPESSystems . . . . . . . . . . . . 38
2.4.1 TheDevelopmentofSpin-ResolvedARPES . . . . . . . . 39
2.4.2 TheDevelopmentofTime-of-FlightARPESSystem . . . . 44
2.4.3 TunableLaser-BasedARPESSystem . . . . . . . . . . . . 46
xi
xii Contents
2.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
3 GrowthofBi2Sr2Ca1−xDyxCu2O8+δ SingleCrystals . . . . . . . . . 51
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
3.2 Bi2212 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
3.3 SingleCrystalGrowthbytheTravelingSolventFloatingZone
Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
3.3.1 PrincipleofTSFZandTSFZFurnace . . . . . . . . . . . . 53
3.3.2 StepsofSingleCrystalGrowth . . . . . . . . . . . . . . . 55
3.4 GrowthofBi2Sr2Ca1−xDyxCu2O8+δ SingleCrystals . . . . . . . 56
3.5 AnnealingofBi2212inHighPressureOxygen . . . . . . . . . . . 62
3.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
4 NodalElectronCouplingintheBi2Sr2Ca1Cu2O8+δ . . . . . . . . . 65
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
4.2 Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
4.3 NodalElectronicStateatLowTemperature . . . . . . . . . . . . . 66
4.4 MomentumDependenceoftheDispersionandSelf-energy . . . . 68
4.5 MDCDispersionandtheQuasiparticleScatteringRate. . . . . . . 71
4.6 TemperatureDependenceoftheElectronSelf-energy . . . . . . . 73
4.7 TheSuperconductingSensitivityofNodalElectronicState. . . . . 74
4.8 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
5 HighEnergyDispersioninBi2Sr2Ca1Cu2O8+δ . . . . . . . . . . . . 83
5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
5.2 Tight-BindingBandStructureCalculation[23] . . . . . . . . . . . 83
5.3 Electron-PhononCouplingSimulation . . . . . . . . . . . . . . . 85
5.4 Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
5.5 MDCandEDCAnalysis. . . . . . . . . . . . . . . . . . . . . . . 87
5.6 TheARPESSpectrainNodalandAntinodalRegion . . . . . . . . 89
5.7 TheMDCandEDCAnalysis . . . . . . . . . . . . . . . . . . . . 89
5.8 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
6 Normal Electron Self-energy and Pairing Self-energy
inBi Sr CaCu O . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
2 2 2 8
6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
6.2 TheSimulationoftheSingleParticleFunctioninSuperconducting
State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
6.3 TheParticle-HoleMixturePresentedinMDC . . . . . . . . . . . 101
6.4 Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
6.5 Particle-HoleMixtureatHighTemperature . . . . . . . . . . . . . 103
6.6 DirectObservationofParticle-HoleMixtureinMDC . . . . . . . 106