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河南师范大学,2012年05月11日薛其坤清华大学物理系拓扑绝缘体:一种新的量子材料MBE Growth and STM/ARPES Study研究生:李耀义王广张童张翼宋灿立程鹏朱燮刚常翠祖王以林蒋烨平文竞毛寒青李志张文号李渭致谢方忠戴希谢心澄(物理研究所/北京大学)张首晟祁晓亮(斯坦福大学/清华大学)沈顺清(香港大学)张绳百(伦斯勒理工学院)牛谦(德州大学奥斯汀分校/北京大学)刘荧(宾州大学)刘朝星(乌兹堡大学)王亚愚朱邦芬(清华大学)清华大学:陈曦贾金锋(上海交大)物理所:马旭村何柯王立莉合作者:科技部、基金委OUTLINE1.拓扑绝缘体简介2.拓扑绝缘体薄膜的分子束外延生长(MBE)及电子结构(Bi2Te3/Bi2Se3/Sb2Te3) 3.扫描隧道显微镜(STM) 研究4.最新进展5. 展望CanMoore’slawkeepgoing?01002003004005000.50.350.250.180.130.10.070.05ActivePowerPassivePower(DeviceLeakage)35025018013010070505005004003002001000Technologynode(nm)Powerdensity(W/cm)2Powerdissipation=greatestobstacleforMoore’slaw!Modernprocessorchipsconsume~100Wofpowerofwhichabout20%iswastedinleakagethroughthetransistorgates.Thetraditionalmeansofcopingwithincreasedpowerpergenerationhasbeentoscaledowntheoperatingvoltageofthechipbutvoltagesarereachinglimitsduetothermalfluctuationeffects.Traffic jam inside chips today微电子学、集成电路发展的瓶颈电子运动过程中受到的散射:芯片发热、速度慢Info highway for chips in the future未来信息高速公路自从近100年前超导量子态被发现以来的一种新的量子态拓扑量子态(拓扑绝缘体)ConductorInsulator材料的分类:能带理论(固体物理的能带论)Topology(拓扑学)拓扑学是近代发展起来的一个研究连续性现象的数学分支。拓扑学主要研究几何图形在连续变换下的不变性质和不变量。g=0g=1foodtoolg=1g=2g=3g=0自由电子(m, e):E=1/2 mV2固体材料中的电子(e, m#):近自由电子近似:E=(ħK)2/2m#E ∝K2抛物线型的能量色散关系ValenceBandConductionBandValenceBandConductionBand一般绝缘体Spin upSpin downE∝K2拓扑绝缘体圆锥形“band twisting”Strong spin‐orbit coupling ConductorInsulatorTopologicalInsulatorInsulating (bulk)conducting (surface)Spin-OrbitalCoupling材料的分类(新):拓扑能带理论g=1g=2g=3g=0对拓扑绝缘体来讲,其性质与其能带拓扑结构有关,与具体细节无关。E∝K的意义?光:E=cp(p=ħk)无质量的狄拉克费米子Graphene:DiracFermionsin2DpcE=石墨烯的电子结构MasslessDiracFermionsEffectivespeedoflightvF~c/300.pcE=FkvE==kxkyEnergyEgSemiconductorBandStructure*222mkE==二维无质量的狄拉克费米体系!GrapheneTI•¼Graphene•Klein Paradox•2DEG without mass•Linear n~E,Linearσ~E,Linear m~E •psudo‐spin•Klein Paradox•Linear n~E,Linearσ~E,Linear m~E •Localization?•Universal σ?Two inequivalent massless Dirac points for each spinorientation, in total four copies of massless Dirac fermionsOdd number of massless Dirac fermionsK'KΓΓSpin=1/2+−EG量子力学预期了“自旋”狭义相对论预期了“自旋轨道耦合”量子力学和狭义相对论Helical Spin Structure of 2D Massless Dirac FermionsFour seasons in a dayOne night in a yearkxkyEQi and Zhang, Phys. Today(2010)Hasan and Kane, Rev. Mod. Phys.(2010)Moore, Nature 464, 194 (2010)……MomentumSpaceInfo highway for chips in the futureRealSpaceSpintronics?1.未来的应用低能耗和高速晶体管自旋电子学器件拓扑量子计算基于拓扑磁电效应的磁存储器件热电效应、催化与能源技术多铁性质与应用探索光学响应及非线性光学后摩尔时代的信息技术?前沿科学研究量子反常霍尔效应/自旋霍尔效应磁单极Majorana费米子分数量子统计(Anyon)拓扑磁性绝缘体Axion研究……Dark matter on your desktop? Wilczek, Nature458, 129 (2009)物质≠反物质(CP不对称)暗物质(轴子)标准模型张首晟、祁晓亮等Science 323, 1184 (2009)磁单极(磁荷)|Ψ1Ψ2=±|Ψ2Ψ1|Ψ1Ψ2=eiθ|Ψ2Ψ1整数量子统计分数量子统计(anyon)电荷+磁荷=任意子(anyon)Majorana费米子费米子:粒子=反粒子Ettore Majorana 1937年提出量子计算:满足非阿贝尔统计的拓扑准粒子进行位置交换操作2DTI:自旋量子霍尔效应inHgTeQW(张首晟Science 2006; Molenkamp Science 2007)5.15.25.35.45.55.65.75.85.96.06.16.26.36.46.56.61.01.50.50.0-0.52.02.53.03.54.04.55.06.05.5(atroomtemperatureinzincblendestructure)adgapeegy(eV)latticeconstanta[臸0正常绝缘体5.15.25.35.45.55.65.75.85.96.06.16.26.36.46.56.61.01.50.50.0-0.52.02.53.03.54.04.55.06.05.5(atroomtemperatureinzincblendestructure)adgapeegy(eV)latticeconstanta[臸0拓扑绝缘体Science杂志:2007年十大科学进展Zhang et al., Nat. Phys. 5, 438 (2009) Strong 3D Topological InsulatorsXia et al., Nat. Phys. 5, 398 (2009) Sb2Te3Bi2Te3Bi2Se3Bi2Se3Δ=0.36eVDefects:•Interstitial impurities•Substitutional impurities•Se/Bi vacanciesBi2Se3 (Bi2Te3 /Sb2Te3)Single crystals1QLTop‐View4.38ÅSeBiSeBiSeSeBiSeBiSeSide‐View1.0nmSe(111) surfacecleaving(stoichiometric)Science 2009Novel Electronic Structure of 3D TI Bi2Te3Fisher (Stanford)Bi2Se3Cava (Princeton)Dirac ConeNat. Phys. 2009Shen (Stanford)Hasan(Princeton)Bulkisn-typeconductorValence BandConduction BandEFGaN:p-dopingGaN/ZnO:highbackgroundcarrierdensity(N-type)Amanoetal.,JJAP28,L2112(1989)Nakamuraetal.,APL64,1687(1994)ZnO:bulkinsulating?N2O2Se2(4)GaZnBiHigh Vapor PressureO‐O: 142 kJ/molN‐N: 167 kJ/molSe‐Se: 172 kJ/molBi2Se3:bulkinsulating?Valence BandO,SevacanciesConduction BandEF(2)BulkInsulatingMaterialdifficult(1) Self‐flux Method for Crystal GrowthSi, GaAs, Sapphire…Thin Films by MBE and MOCVD?OUTLINE1.拓扑绝缘体简介2.拓扑绝缘体薄膜的分子束外延生长(MBE)及电子结构(Bi2Te3/Bi2Se3/Sb2Te3) 3.扫描隧道显微镜(STM) 研究4.最新进展5. 展望人类首次:9“看到”单个原子、分子9“操纵”单个原子、分子1986年诺贝尔物理学奖扫描隧道显微镜:由瑞士科学家Binnig和Rohrer博士于1981年发明MBE‐STM(Molecular Beam Epitaxy‐Scanning Tunneling Microscope)(分子束外延-扫描隧道显微镜)GaAs4Se4FetipsampleAMBE + LT‐STM System (Unisoku)STM/STS: 400 mKMagnetic field: 11 TVacuum: 5x10‐11TorrMBEcryostatSTM高的能量分辨本领20MLPbThinFilmsResolution: 0.1 meVJi etal., PRL 100, 226801 (2008)Chen et al., PRL 101, 197208 (2008)Fu et al., PRL 103, 257202 (2009)Zhang et al., PRL 103, 266803 (2009)Cheng et al., PRL 105, 076801(2010)Zhang et al., Nat. Phys.6, 104 (2010)Song et al., Science 332, 1410 (2011)Li et al., Nature Physics (2011) •STM/STS: 4K•ARPES: 1meV•RHEED•5x10‐11TorrMBE‐STM‐角分辨光电子能谱System STMMBEARPESPhoton energy: 21.2eV(HeI) Energy resolution: 10 meVAngular resolution: 0.2°T=77 KExperimental parametersLayer‐by‐Layer Growth of Bi2Se3(Bi2Te3) on SiSiwaferReal‐T
本文标题:拓扑绝缘体-薛其坤学术报告
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