凝聚态物理前沿讲座方忠QuantumSimulationintheFieldofSpintronic.pptx

8/2/2024方方 忠忠中国科学院物理研究所，理论室中国科学院物理研究所，理论室 Quantum Simulation in the Field ofSpintronics and OrbitronicsAcknowledgement:Y.G.Yao,K.Terakura N.Nagaosa Y.Tokura凝聚态物理前沿讲座凝聚态物理前沿讲座第1页8/2/2024 Contents 1.Quantum simulations based on DFT (1)Simple introduction to first-principles calculations (2)Our method,code,and computer facilities 2.Dissipationless quantum current for spintronics (1)Anomalous Hall Effect (2)Spin Hall Current (3)Anomalous Nernst Effect 3.Orbiton and Orbitronics (1)Phase diagram of La1-xSrxMnO3 (2)Orbital-dependent phase control in Ca2-xSrxRuO4 (3)Magnetism in double perovskites 4.Surface of transition-metal oxides第2页8/2/2024Quantum Simulation based on DFTAtoms+electronsElectronsMany-bodyElectronsSingle-particleDensityFunctionalAdiabatic ApproximationHohenberg-KohnKohn-ShamHellmann-FeynmanForce and StressMDSCF第3页8/2/2024Self-consistent Solver for KS problemSCFLDAGGALDA+U第4页8/2/2024LDA+U method第5页8/2/2024Pseudopotential SchemeNormal-conservingPseudopotentialUltra-SoftPseudopotential第6页8/2/2024Virtual Crystal Approxmation(VCA)For virtual atomsSolve Schrodinger equationIonic unscreened potential第7页8/2/2024How to solve the single particle problem Real Space (no FFT)Finite element Finite difference Multi-grid Adaptive Wavelet Reciprocal Space (with FFT)LACO LMTO FLAPW PAW Plane-wave Greens function Pseudopotential,ASA,第8页8/2/2024Other Problems in Simulations1.Exchange-correlation functional2.Strongly-correlated systems3.Force calculation&Molecular dynamics4.Magnetic,optical&electronic properties5.Excited States6.Non-equilibrium&Time-dependent process7.Order(N)method&Large scale8.Catalysis,Chemical reaction,Bio-systems9.第9页8/2/20241.First-principles calculations based on DFT2.Plane-wave basis3.Ultra-soft Pseudo-potential4.LDA,GGA,LDA+U,etc5.Virtual crystal approximation(VCA)6.Real space RMM for larger systems7.Full parallelization by MPI8.SGI,IBM-SP,Alpha,Cray,VPP,PC-ClusterOur Method第10页8/2/2024 STATE Code:(Simulational Tool for Atom Technology)Main Contributors:Z.Fang,Y.Morikawa,T.Ikeda,H.Sawadaand other JRCAT membersFor details:Z.Fang,et.al,J.Phys:Cond.Matt.,14,3001().(review article)100,000 lines,Accuracy 1meV/Atom,200 atoms.Widely used in Japan,Taiwan,Korea,Denmark,etc.第11页8/2/2024IBM SP690,64 CPUs,128G,1T-disk第12页8/2/2024Three Characters of Electron Charge Spin Orbitalwell known “hot”topic newExtensively used being used will be usedI,V,Charge currentCharge excitation spin wave orbitonCharge current spin current movement anisotropy functionality .第13页8/2/2024SpintronicsThe electron has both charge and spin.Mostly only the charge property is used.Energy scale for the charge interaction is high,1eV,energy scale for the spin interaction is low,10-100 meV.Much lower power consumption for spin-based device.Spin-based electronics also promises a greater integration between the logic and storage devices第14页8/2/2024Problems for Spintronic devices spin injection into semiconductor Ohmic injection from ferromagnet Low efficiency(Difficulty):Ferromagnetic metal:conductivity mismatch spin polarization is almost lost at interface.Ferromagnetic semiconductor (e.g.Ga1-xMnxAs):Curie temperature much lower than room temp.Ferromagnetic tunnel junction.spin detection by ferromagnet spin transport in semiconductor spin relaxation timeOptical pump and probe第15页8/2/2024Only two known examples of dissipationless transport in solids!Supercurrent in a superconductor is dissipationless,since London equation related J to A,not to E!Vector potential=odd under T,charge current=odd under T.In the QHE,the Hall conductivity is proportional to the magnetic field B,which is odd under T.Laughlin argument:all states below the fermi energy contribute to the Hall conductance.Streda formula,TKNN formula relates the Hall conductance to the 1st Chern number.第16页8/2/2024New dissipationless transport in solidsdue to spin-orbital coupling!Anomalous Hall Effect(charge current):1 T.Jungwirth,et.al.,PRL,88,207208();2 Z.Fang,et.al,SCIENCE,302,92()3 Y.G.Yao,et.al,PRL,92,37204();4 W.L.Lee,et.al,SCIENCE,303,1647()Conventional:xy =R0H +4RSM Intrinsic Mechanism:xyxy(M)Thus Jx=xyEy is T invariant J is odd,E is even,M is odd Dissipationless spin Hall current:1 S.Murakami,et.al,SCIENCE,301,1348();2 J.E.Hirsch,et.al.,PRL,83,1834(1999)3 J.Sinova,et.al,PRL,92,126603()4 S.Q.Shen,et.al.,cond-mat/040305.5 Y.Xiong&X.C.Xie,cond-mat/0403083.Spin current is even under T第17页8/2/2024BjHFMjAHEConventional HallAnomalous HallEESpinjSHEESpin Hall第18页8/2/2024Merit of AHE and SHE 1.It works because of spin-orbital coupling,which is active even at room T.2.It is entirely topological(dissipationless).第19页8/2/2024 Spin-Orbital Coupling Berry Phase Magnetic Monopoles in Momentum SpaceAnomalous Hall current and Spin Hall current (Both are dissipationless)Intrinsic Mechanism第20页8/2/2024Effective Hamiltonian for adiabatic transportEquation of motion(Dirac monopole)Drift velocityTopological termNontrivial spin dynamics comes from the Dirac monopole at the center of k space,witheg=l:Adiabatic transport=potential V does not cause inter-band transitions only retain the intra-band matrix elements 第21页8/2/2024Full Quantum Calculations Based on Kubo FormularAnomalous Hall conductivitywithSpin Hall conductivityJys第22页8/2/2024Conserved Spin Current(S.Murakami,et.al.,cond-mat/0310005)Conserved spinwhich satisfydefine current i,n,m =band index,=kramers doublets index第23页8/2/2024ZFang,et.al.,SCIENCE 302,92()反常反常HallHall效应与动量空间中磁单极效应与动量空间中磁单极第24页8/2/2024Calculated Gauge Flux for kz=0 in SrRuO3bz(kz=0)GMMMMZ.Fang,et.al,SCIENCE,302,92()第25页8/2/2024SrRuO3第26页8/2/2024SrRuO3第27页8/2/2024Calculated Spin Hall Current in GaAs第28页8/2/2024Calculated Spin Current for GaAs and SnTe第29页8/2/2024One Example for Half-MetalMnAs第30页8/2/2024Fully spin polarized anomalous Hall current in MnAsSpin conductivityAHE conductivity第31页8/2/2024Anomalous Nernst EffectBVFMVConventionalAnomalous第32页8/2/2024Inverse Anomalous Nernst Effect:Cooling and refrigeratorFMHeat current jQExHeat current:Eq.of motion:第33页8/2/2024egt2g3z2-r2x2-y2xyyzzxOrbitronics第34页8/2/2024Orbital Degrees of Freedom(ODF)EnergyDown spinUp spinEFO-2pO-2pt2gt2gegeg2-fold(ODF)3-fold“Half-metal”第35页8/2/2024Various OrderingsFMA-typeC-typeG-typeLatticeSpinChargeOrbitalSC,TMR,CMR,M-I Transition,Anomalous Hall Effect,Magneto-optical,Ferroelectricity,Piezoelectricity,etc 第36页8/2/2024ExperimentalTheoreticalSCIENCE 288,462().J.Phys.Soc.Jap.68,3790(1999).Phase Diagram of Tetragonal La1-xSrxMnO3(Controlling of Orbital and Spin Orderings)Z.Fang&K.Terakura,PRL 84,3169().第37页8/2/2024FMA-AFC-AFG-AFOrbital and Spin OrderingsPhysics:Spin Orbital Lattice Double exchange Super-exchange Compression Less conductivity第38页8/2/2024Electric-Field-induced Orbital SwitchingK.Hatsuda,APL 83,3329().第39页8/2/2024LatticeSpinChargeOrbitalElectronic Structures of Ca2-xSrxRuO4EnergyDown spinUp spinEFO-2pO-2pt2gt2gegeg3-fold第40页8/2/2024Ca2-xSrxRuO4:Isovalent substitution Rotation Rotation Rotation +Tilting Tilting +CompressionAF MottInsulatorNearlyFM MetalS.Nakatsuji,et al.,PRLO.Friedt,et al.,PRB第41页8/2/2024Issues:(1)How to understand the complicated phase diagram.(2)Whats the rule of orbital.第42页8/2/2024Effects of Structure DistortionsZ.Fang&K.Terakura,PRB64,R20509()Rotationxy orbitalVHSFMTiltingyz,zxnestingAF第43页8/2/2024Occupations and MagnetizationsZ.Fang et al.PRB().第44页8/2/2024Orbital Phase Diagram of Ca2-xSrxRuO4CaSrDoping x0.0 0.2 0.5 2.0EEfxyyz,zxEEfxyyz,zxEEfxyyz,zxxyxy ferro-orbital orderingAF,S=1 from yz,zxFM,S=1/2 from xyItinerant yz,zx with small SNM stateWith VHS from xy1.J.H.Jung,Z.Fang,et.al.,PRL 91,056403().2.Z.Fang,et.al.,PRB 69,045116().第45页8/2/2024110RuO6 八面体在表面旋转八面体在表面旋转Sr2RuO4表面电子结构表面电子结构LEEDSTM1.R.Matzdorf,Z.Fang,et.al.,SCIENCE 289,746().2.Z.Fang,et.al.,PRB 64,R20509()第46页8/2/2024PDOS of various doping x第47页8/2/2024Exp.XASCalculated XAS90K300K第48页8/2/2024Optical conductivityExperimentsCalculationsJ.H.Jung,Z.Fang,et al.PRL().第49页8/2/2024FeFeMSr2FeMO6(M=Mo,W,Re)8 1.Why Tc is so high for M=Mo,Re?2.Why M=W case is AF insulator?第50页8/2/2024EFd statesd statesMajority spinMinority spinMo d stateor other p statesFMZ.Fang,et.al.,PRB 63,R180407()EFd statesd statesMajority spinMinority spinMo d statesor other p statesAFNew Mechanism for Sr2FeMO6 and(Ga1-xMnx)As第51页8/2/2024Fe(t2g)SpinEF M(t2g)(M=Mo,Re)Fe(t2g)Electronic Structure of Sr2FeMoO6第52页8/2/2024Surface of SrTiO3 with Oxygen Vacancy Important substrate Surface gas sensitivity Ferroelectricity Catalytically active第53页8/2/2024STMSTST.Kubo,et.al.,PRL 86,1801()H.Tanaka,et.al.,Jpn.J.Appl.Phys.32,1405(1993)第54页8/2/2024第55页8/2/2024StructureChargeMagnetizationSrOTiO2Sr Ti OLDA+USurface of SrTiO3 with oxygen vacancy (Spin polarized surface)Z.Fang,et.al.,Surf.Sci.Lett.470,L75()第56页8/2/2024第57页8/2/2024SrO termination(GGA)TiO2 termination(GGA)262626TiO2 termination(LDA+U)5 x 5 STM of SrTiO3 surface第58页8/2/2024100100001001SurfaceCentral（La,Sr)O terminationMnO2 terminationMnOrbital polarization on the surfaces of La1-xSrxMnO3Z.Fang,et.al.,J.Phys.Soc.Jpn.70,3356().第59页8/2/2024 SummaryQuantum Simulation Charge Spin Orbital(Electronics)(Spintronics)(Orbitronics)Problems:1.Efficient method for cross-correlated systems 2.Towards large scale(surface&interface)3.Accurate method for many-body systems第60页