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Masahiro YAMASHITA (Tohoku University) lectrical Conductivities and Kondo Peak of Single-Molecule Magnets

Masahiro YAMASHITA

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Electrical Conductivities and Kondo Peak of Single-Molecule Magnets. Masahiro YAMASHITA. (Tohoku University). Outline ○ Conducting Single-Molecule Magnets (SMMs). ○ Memory Device in Pc Multi-Decker Ln SMMs ○ Kondo Peak of Double-Decker Pc2Ln SMMs - PowerPoint PPT Presentation

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  • Masahiro YAMASHITA(Tohoku University) Electrical Conductivities and Kondo Peak

    of Single-MoleculeMagnets

  • Outline

    Conducting Single-Molecule Magnets (SMMs) Memory Device in Pc Multi-Decker Ln SMMs

    Kondo Peak of Double-Decker Pc2Ln SMMs

    Field Effect Transistor (FET) of Double-Decker Pc2Ln SMMs-----------------------------------------------------------------------------------------

    DMET-CuCl2 : Superconductor

    DMET-MCl4 : M-I Transition

    BEDT-TTF Coordinated-CuBr CT Complexes

  • What is Single-Molecule Magnets ?

  • Single Molecule Quantum Magnets, SMMs

    Multinuclear nano-cluster metal complexes A single molecule behaves like a magnet Quantum tunneling effect Frequency dependent ac susceptibility Cole-Cole plotHeat CapacityUni-axis anisotropy+Isolated molecules

  • Mn12O12(O2CR)16(H2O)4: S = 10ms = +10ms = 0ms = -10D/kB= |D|S2D/kBQuantum Dots: Single Molecule Magnets Hendrickson, D. N.; Christou, G. et al, J. Am. Chem. Soc., 1988, 110, 8537.Gatteschi, D. et al, Science, 1994, 265, 1054.Quantum spin tunneling

  • MagnetsBulk MagnetsQuantum Magnets@ ClustersNano-DotsS = 3, 9, 10.Anisotropy6.02 x 1023 bit/molDS2@ Ising 1-D ChainsNano-WiresTuning of S and JLarge AnisotropyJ+D)S2Increase of the capacity2-D and 3-D Networks8 x 109 bit (1GB)Development of the propertyMolecular memoryQuantum computing device

  • Basic Science

    Multi-FunctionalQuantum Molecular Magnets

    One Memory Storage into One Single-MoleculeMagnet

    DNA Quantum Computer

    SMMs and SCMs FETApplied Science

  • Multi-Functional Molecule-Based Nano-MagnetsConductivityPorosityOpticsFerroelectricsChiralityQuantum Magnets

  • e-SMMSMMDEHigh Tc Quantum GMR (S=10, 20, 30)Quantum Spintronics

  • Strategy Segregated structure[Ni(dmit)2]-SMMConducting layer[Mn4(hmp)6(CH3CN)2(H2O)4](ClO4)42CH3CN4+2+[Mn2(5-MeOsaltmen)2(MeCN)2](PF6)2[Pt(mnt)2]-Conducting layer

  • MnIIMnIIMnIIIMnIIIStrategySMM=Double-cuboidaltetranuclear manganese cluster

    [Mn4(hmp)6Br2(H2O)2]Br2(ST = 9, MnII2MnIII2)

    G. Christou et al. Inorg. Chem. 2001, 40, 4604.organic conductor=[Pt(mnt)2]-

  • Mn4 SMMConductor Pt(mnt)2-Electrochemical oxidationSynthesis of the Compound constructed from Mn4 and [Pt(mnt)2]x-[Mn4(hmp)6(MeCN)2][Pt(mnt)2]6(2)[Mn4(hmp)6(MeCN)2][Pt(mnt)2]42(MeCN) (1)L. Lecren, et. al, J. Am. Chem. Soc. 2005, 127, 173534+

  • c-axis directionPacking Veiw of [Pt(mnt)2]6[Mn4(hmp)6(MeCN)2]a-axis directionb-axis direction

  • Conductivity of [Mn4(hmp)6(MeCN)2] [ Pt(mnt)2]6Activation energy 136 meVs = 2.210-1 S cm-1 (r.t., 4-probe method)

  • Molecular Superconductors Based on Metal Dithiolene Complexes Conducting SMMNi(dmit)2-M(saltmen)- dimer SMM[Mn2(5-MeOsaltmen)2(MeCN)2]2+

    H. Miyasaka, et. Al., Angew. Chem. Int. Ed., 43, 2801(2004)R. Kato, Chem. Rev. 2004, 104, 5319-5346

  • Synthesis of [Mn2(5-MeOsaltmen)2(MeCN)2][Ni(dmit)]74(MeCN) (3) [TBA][Ni(dmit)] + [Mn2(5-MeOsaltmen)2(MeCN)2]PF6 + TBAPF6Electrochemical oxidationFormula weight 4280Temperature / K 100Crystal system triclinicSpace group P-1a / 12.0675 b / 12.1753 c /26.5789 a / 88.762 b / 79.746 g / 88.047V / 3 3840.03Z =1R1 = 0.0613, wR2 = 0.1602GOF = 0.997Coexistence of [Mn2(5-MeOsaltmen)2]2+ and non-integer [Ni(dmit)2]0.29-

  • Packing Veiw of [Mn2(5-MeOsaltmen)2(MeCN)2][Ni(dmit)]74(MeCN)

    a-axis direction2-D conductor (ab plane) abca-axis direction =2.78 S cm-1

    c-axis direction =0.03 S cm-1

  • DC and AC magnetic susceptibilityJahn-Teller axis

  • s =2.78 S cm-1 (4-probe300 K)Activation Energy = 119 eVConductivity of [Mn2(5-MeOsaltmen)2(MeCN)2][Ni(dmit)]74(MeCN) ab

  • [Mn2(5-MeOsaltmen)2{Ni(dmit)2}2](1)[Mn2(5-Mesaltmen)2{Ni(dmit)2}2](2)New structure of SMM-Conductor; Coordinated {Ni(dmit)2}1-

  • [Mn2(5-MeOsaltmen)2{Ni(dmit)2}2](1)[Mn2(5-Mesaltmen)2{Ni(dmit)2}2](2)Stair-like column & major distancesConductivity1; 7 x 10-4 S cm-1 (r.t.)2; 1 x 10-4 S cm-1 (r.t.)Activation Energy1; 182 meV2; 292 meV

  • Magnetism (DC)[Mn2(5-MeOsaltmen)2{Ni(dmit)2}2](1)[Mn2(5-Mesaltmen)2{Ni(dmit)2}2](2)Ferromag. Int.Unpaired-electron occupying dz2 orbital3pp orbitalOrthogonalAntiferro. Int.Overlap Ideal out-of-plane dimer model J > 0 (SMM) out-of-plane dimer model J > 0 intra-dimer ferromagnetic interaction out-of-plane dimer model J < 0 intra-dimer antiferromagnetic interaction

  • [Mn2(5-MeOsaltmen)2{Ni(dmit)2}2](1)Magnetism (AC)t0 = 8.2 x 10-7 sDeff/kB = 11.4 K (1500 Oe)SMM propertyActivation energy 119 meVs = 7 x 10-4 S cm-1 (r.t.)Transport propertySemiconductiveSurpressed point(1500 Oe)New type SMM-Conductor: [Ni(dmit)2]1- moiety mediate magnetic interaction and conductivityAC measurement under various fieldArrhenius plot

  • [Ni(chxn)2Br]Br2 Iwai et al. Phys. Rev. Lett. 057401(2003).Photo-induced Insulator to metal transition in 1D Ni complexDrudeMott insulator MetalNiBrNCbInsulator(before excitation)Insulatormetal2 psdz2(Ni)J=3000K pz( Br)

  • [Mn2(5-Rsaltmen)2(L)2]2+Ni(dmit)2Ultrafast optical responses in Molecular magnet1D electronic system(Mott insulator) [-1 cm-1]E // 1D Axis(Charge gap)E 1D Axisi) Photo-induced insulator Metal transition mid-IR pump-probe spectroscopyii) Photo-modulation of magnetic property pump-probe (Kerr rotation) Interaction between 1D electronic systemand molecular magnetMolecular magnetPhoto excitation of charge1.55 m

  • psPhoto excitation of charge metallization of the Mott insulatorPhoto-induced I-M transition in Molecular magnet1D electronic system(Mott insulator)Molecular magnetUltarfast responsedecay 1ps0.1 ps0.15 mJ/cm2pump

  • Ultrafast control of magnetic property of molecular magnet/2polarlizarbalanced detection of Kerr rotation anglePumpProbeSampleBPhoto excitation of charge change of the spin state ?ps1D electronic system(Mott insulator)Molecular magnetresponse of M

  • Basic Science

    Multi-FunctionalQuantum Molecular MagnetsOne Memory Storage into One Single-MoleculeMagnet

    DNA Quantum Computer

    SMMs and SCMs FETApplied Science

  • The dream

  • information storage at the molecular level ! HSM upThe dream

  • Nanosciences a challenge for chemists and friends HSM up

  • Phase lag phenomena for (TBA)[TbIIIPc2] (PcH2 = Phthalocyanine)(TBA)+[TbIIIPc2]- shows maximum at 40 K in cM at 1kHz AC magnetic field.N. Ishikawa, M. Sugita, T. Ishikawa, S. Koshihara, and Y. Kaizu, J. Am. Chem. Soc., 2003, 125, 8694-8695. Blue : Diluted with YIII. (TbIII : YIII = 1:4)Red : (TBA)[TbIIIPc2]

  • Upward temperature shift of the phase lag phenomena by ligand oxidation.Oxidation upwards the temperature region for phase lag phenomenon from 40 to 50 K.N. Ishikawa, M. Sugita, N. Tanaka, T. Ishikawa, S. Koshihara, and Y. Kaizu,Inorg Chem., 2004, 43, 5498 - 5500. [TbIIIPc2]-1Anionic complex[TbIIIPc2]0Neutral complex

  • [TbPc2]0

    Potential BarrierD = 410 cm-1

    Relaxation Timet0 = 1.5 10-9 s

    Brocking TemperatureTB = 50 K [TbPc2]-TBA+

    Potential BarrierD = 230 cm-1

    Relaxation Timet0 = 2.0 10-8 s

    Blocking TemperatureTB = 40 KChange of SMM Properties from Anions to Neutral

  • StrategySingle-Molecule Memory of SMM TbPc2Spin-Polarized STM (/) In-Put/ Out-PutDirect Access to TbPc2 SMM bySpinPolarized STMSingle-Molecule = bit 0-DFabricationHuge Memory Storage

  • Crystal Structutres (Rigaku CCD Saturn70 at 93 K) CrystallizationCHCl3/HexDark Green Needles orthorhombic, P212121

    Molecular Sizediamiter1.6 nm height0.4 nm Twisted Angles41.4o41.4oTbPc2YPc2DyPc2

  • STM of [Pc2TbIII]at room temperature

  • STM image for [TbPc2]0 at 4.8 KSTM image of [TbPc2]0 isolated molecules on Au(111) surface ObservationLUMO of [TbPc2]0

  • TbPc2: Near the Fermi level V = 0 VKONDO peak KONDO effectThe Coupling with Magnetic Impurities and Conducting ElectronsSTSScanning Tunneling Spectroscopy: TbP2/ Au(111)55 nmSample biasSTMkBTK: Binding Energy 80 KKONDO Temperature (TK) 80 KFWHM:7 meV Measure Pointscenter outside SharpeMagnetic Impurities : Tb3+ (S = 3) and p-Electron (S = 1/2) Metal Center ChangeDy3+(S = 5/2) and Y3+S = 08

  • Structures of Tb-multiple-deckerPc CompoundsDouble-deckerTriple-deckerQuadruple-deckergreen (solution) black crystalSMM(TB = 24 K)blue (solution)black crystalSMM(TB = 24 K)blue (solution)black crystalSMMTB = 24 K

  • triclinic, P-1, blacka = 1.31648(11) nm, b = 1.78266(17) nm, c = 2.06226(19) nm, a = 107.2150(10)o, b = 90.5010(10)o, g = 100.8480(10)o V = 4.5296(7) nm3, Z = 1, R1 = 0.0465, wR2 (all) = 0.1337Crystal structure of Tb2Pc3 (Rigaku CCD Saturn70 at 93 K) RecrystallizationCHCl3/EtOH Space grouptriclinic, P-1 molecular size2.4 nm 0.7 nm stacking angle between two Pc 32o TbTb: 0.352 nm

  • Magnetic SusceptibilitiesMagnetization under Magnetic FieldTb3+(1 mol) 11.82 Double-decker ~10Triple-decker ~20Quadruple-decker ~30cmT/cm3 K mol-1Tb3+(1 mol) 9(sat.) Double-decker 4.5Triple-decker 9.8Quadruple-decker 13.5Ms/NmBcmTIncreaseIncreaseMagneticBehaviors of Tb-multiple-deckerPc ComplexesTb3+1Tb3+Tb3+Tb3+Tb3+Tb3+1

  • TB=24KTB=24KTB=24KDouble-deckerTriple-deckerQuadruple-deckerAC Magnetic Susceptibilities of MultipleDeckerTbComplexes

  • Basic Science

    Multi-FunctionalQuantum Molecular MagnetsOne Memory Storage into One Single-MoleculeMagnet

    SMMsand SCMs FET

    DNA Quantum ComputerApplied Science

  • Quantum Field Effect Transistor (FET)Schematic draw of FET device used in the present measurement[Pc2Tb]Carbon paste

  • p-Typen-Type

  • p-Type

  • Energy diagram for (TBA)[LnIIIPc2]Why the slow magnetization relaxation is observed for the Tb and Dy complexes ?Phase lag phenomenacM maximumLarge gap between MJ = 6 and 5Only TbIII and DyIII complexesElectronic Configuration Tb0 : [Xe].4f9.6s2TbIII: 4f electron 8 S = 3, L = 3, J = S+L = 6 TbPc2Large magnetization reversal barrier energy

  • FIELD-INDUCED SDW PHASE AND SUPERCONDUCTIVITY OF (DMET)2CuCl2H. Ito1, Y. Yokochi1, D. Suzuki1, H. Tanaka1, S. Kuroda1, K. Enomoto2, S. Uji2, M. Umemiya3, H. Miyasaka3, K. -i. Sugiura3, M. Yamashita3, H. Nishikawa3, K. Kikuchi3, I. Ikemoto3 1Department of Applied Physics, Nagoya University, Chikusa, Nagoya, 464-8603, Japan2National Institute for Materials Science, 3-13, Sakura, Tsukuba, Ibaraki 305-0003, Japan3Department of Chemistry, Tokyo Metropolitan University & CREST, 1-1 Minami-Ohsawa, Hachioji 192-0397, Japan

  • Unsymmetrical Donor : DMET BEDT-TTFTMTSFDMET1-D Conductor(CDW, SDW, Metallic)2-D Conductor(Metallic, Superconductivity)Q-1-D Conductor(CDW, SDW, Metallic, Superconductivity )Various Electronic States

  • DMET stack in along b-axisCuCl2DMET(DMET)2CuCl2Slow diffusion of MeOH solution of CuIICl2 (2.5 mL, 8.9 mM) into THF solution of DMET (2.5 mL, 1.9 mM)1mm crystal in a week

  • (DMET)2CuCl2 band calculationtb=0.28eVta=0.048eVSe I(Ryd) 4s 2.112 -1.47 4p 1.827 -0.809S 3s 2.122 -1.62 3p 1.827 -0.77Hckel parameters (after R. Kato)Transfer integrals along 1D and perpendicular to 1D axistb/ta5.8

  • (DMET)2CuCl2Conduction and SuperconductivityRT ~ 400 S/cmRRR~200bc= 7000b axis resistivitySuperconducting transitionat 0.8 KRcHc* axis resistivity

  • (DMET)2CuCl2 Field-induced SDW transitionsHWe observe FISDW transitions below 4 K and above 4 T, showing step-like Hall voltages with sign reversals (DMET)2I3 by Uji at al.Critical magnetic fields aresmaller for (DMET)2CuCl2than (DMET)2I3

  • ThermopowerS(300K) = +25 mV/KVConstantanCuCuAu wireAg pasteCu wireheaterbH.Yoshino et al., PR B 67(2003) 035111givestb=0.207 eV, smallerthan that of band calculation7.607.55, =1.5b=7.586CuCl2Metallic positive thermopower

  • Classification of (DMET)2X family 1.X=PF6As6Semiconducting2.X=BF4ClO4 MI transition at 100-200 K 3.X=Au(CN)2AuCl2AuI24.X=I3AuBr2MetallicAu(CN)2AuCl2AuI2Tc [K]1.13.5kbar0.830.555kbarI3AuBr20.47SDW at low temperatureSuperconductivity under pressureMetallic 1.91.61.5kbarta/tb0.1030.1000.102FISDWSuperconductivity at ambient pressureKeizo Miura et al., J. Molec. Electr. 4 (1988) 173CuCl2CuCl20.80.10IBr20.5823023030017021014400sRT [S/cm]

  • Lebed resonances Third Angular EffectTransfer integral ratio of ta/tb=0.10SummaryNew Q1D conductor (DMET)2CuCl2FISDW transitions above 4 T Step-like Hall voltages with sign reversals 1Superconducting transition at 0.8 K, 0 kbarThermopower Transfer integral tb=0.207 eV

  • Metal-Insulator Transition and p-d Interaction of Quasi-1D Organic Conductors (DMET)4(MCl4)(TCE)2 (M=Mn,Co,Cu,Zn)

    Hiroshi Ito1 Daichi Suzuki1, Harutaka Watanabe1, Hisaaki Tanaka1, Shin-ichi Kuroda1, Masamichi Umemiya2*, Shinya Takaishi2,Hitoshi Miyasaka3, Ken-ichi Sugiura3, Masahiro Yamashita2,4 , Hiroyuki Tajima5, Eiji Ohmichi5, Toshihito Osada5

    1Department of Applied Physics, Nagoya University2Department of Chemistry, Tohoku University 3Department of Chemistry, Tokyo Metropolitan University4CREST5Institute of Solid State Physics, University of Tokyo*Present address, Dept. Mater. Sci., University of Hyogo

  • Group 1 : Octahedral anion (X = PF6, AsF6) semiconducting behaviorGroup 2 : Tetrahedral anion (X = BF4, ClO4, ReO4,) metal-insulator (MI) transition (SDW) X=FeBr4, FeCl4 p-d interaction (Enoki, et al. 2003)Group 3 : Gold dihalide anion (X = AuCl2, AuI2, Au(CN)2) MI transition (SDW) superconducting under pressureGroup 4 : Linear halide anion (X = I3, I2Br, IBr2, SCN, AuBr2*) X = I2Br, SCN, AuBr2 metallic behavior X = I3, I2Br superconducting X = I3 FISDW (Field Induced SDW) phase. X=CuCl2 superconducting and FISDW phase (Ito, et al. 2005) Group 5 : Linear anion (X = AuBr2*) k-type packing with superconducting transitionThe unsymmetrical donor, DMET, has produced semiconducting, metallic, and superconducting salts [Kikuchi, Murata et al.]

    DMET salts DMETGroup 6 : Cr complexes (X=Cr(L)n(NCS)4) (Umemiya et al. 2006)

  • Structure of (DMET)4MCl4(TCE)2All salts (M=Mn, Co, Cu, Zn) are isostructural.Short contacts between donors and MCl42- anions.

    stacking along a+bM=Mn Cl(2)-S(8) : 3.507(3) Cl(3)-S(2) : 3.296(3) M=Co Cl(1)-S(9) : 3.315(3) Cl(2)-S(15) : 3.506(3) M=Cu Cl(1)-S(9) : 3.456(3) Cl(2)-S(15) : 3.548(3)

  • -1.0eV1.0eVEFGYVXGGVXYp-electron electronic structuresTight-binding band calculation based on HOMOs of DMET moleculesOriginal Brillouin zone1. Unit cell contains 4 DMET molecules.

    The Brillouin zone is a half of that of usual Q1D DMET salts.

    3. Planar Fermi surface are folded into semimetallic one.In the extended Brillioun zoneelectron-likehole-likesemimetallic Fermi surface2.5% of 1st BZ

  • M = MnM = CoM = CuM = ZnTemperature / K10020030010-310-210-1010010110-4Temperature / K1002003000Resistivity / cm10-310-210-110010110-4Resistivity / cmMetal Insulator transitions at TMIM=Mn, Cu metallic at 7 kbar M=Co, Zninsulating phase remains at 7 kbar Intralayer resistivity

  • Large magnetoresistance with hysteresis is observed. Width of hysteresis in M=Zn is larger than that of M=Co. Weak oscillations are observed above 30 T.I // B // c-axis longitudinal magetoresistance

  • Small magnetoresistanceNo hysteresis No oscillationClear Shubnikov-de Haas oscillations of frequency ~225 TNo hysteresis~225TI // B // c-axis longitudinal magetoresistanceM = MnM = Cu

  • Reflectance spectra of M=Mn and M=Zn are almost identical, showing a typical Q1D metallic one.

    M=Co has slightly moderate raise at the edge, which is attributable to the difference of g .

    The edge of M=Cu is obscure.Drude modelFrom the plasma frequency, Q1D transfer integrals of t//=0.25 eV, t=0.03 eV are deduced.

  • On the mechanism of metal-insulator transitionLarge magnetoresistance with hysteresis is reminiscent of FISDW. The metal-insulator transition is understood in terms of the SDW transition by the imperfect nesting of the semi-metallic Fermi surface, like (TMTSF)2NO3. Resulting small pockets cause hysteresis and SdH-like oscillations.Variety of the transport behaviors among these salts stems from the presence of magnetic ions. Next we look into magnetic properties of these salts. Remaining Small pocketFirst-order transitionsbetween field-induced phases cause hysteresisImperfectnesting

  • Magnetic field: 10 kOeSQUID dc susceptibility (M=Mn,Co, Cu) antiferromagnetic interactions mediated by p-electronsT - qcc =Curie Weiss lawc T (emu K mol-1)c / emu mol-1c T / emu K mol-11/c / mol emu-1

  • Metal-insulator transition is ascribed to an imperfect nesting of semimetallic Fermi surface.Peculiar behaviors, suppressed magnetoresistance of M=Mn, anisotropic resistivity of M=Cu, are the results of p-d interactions.

    MnCuCoZnTransport propertyTMI=25KTMI=5-20K (Intralayer semiconducting)TMI=15 KTMI=13 KMagneto-resistancesmalllarge withSdHlarge withhysteresislarge withhysteresisp-d interaction

  • (DMET)4MCl4(TCE)2 (M = Mn, Co, Cu, Zn) All salts are isostructural, having semimetallic Fermi surface. Mn, Co, Cu, Zn salts exhibit metal-insulator transitions at 25 K, 15 K, 5-20 K and 13 K, respectively. Cu salt shows anisotropic behavior of resistivity; intralayer is semi-conducting, but interlayer is metallic. Co and Zn salts show large magnetoresistance with hysteresis is observed salts, with weak oscillations above 30 T. Cu salt shows clear SdH oscillations. For Mn, magnetoresistance is suppressed. Co and Zn salts show p-electron ESR signal, which disappers at TMI. In Mn, Co, Cu salts, dc susceptibility shows Curie-Weiss behavior. Mn and Cu ESR signals show exchange narrowing.

  • ELECTRICAL CONDUCTION IN DIVALENT BEDT-TTF SALTSH. Ito, Y. Yokochi, H. Tanaka, S. Kuroda Department of Applied Physics, Nagoya University

    R. Kanehama, M. Umemiya, H. Miyasaka, K. -i. Sugiura, M. Yamashita Department of Chemistry, Tokyo Metropolitan University & CREST

    H. Tajima, and J. YamauraInstitute for Solid State Physics, University of Tokyo

  • Introduction. Charge-transfer salts of TTF derivativesConducting layerMagnetic layerConducting propertyMagnetic propertyVarious conducting propertiessemiconductormetalsuperconductortype-I d- system1973 (TTF)(TCNQ) synthesized: first organic metal J. Am. Chem. Soc., 95, 948 (1973)Introduction of magnetic d-electronsCounter ionMetal ionNo d- interaction

  • Syntheses. Diffusion Methodredox reactionBEDT-TTF (ET) / THF, DCM, DCE, TCE...CuIIBr2 / MeOHSeveral weeks of diffusion . . .em-1, tb-1, tb-2, cb-1, cb-2, cb-3Coordination Sites of ET-ligands. BEDT-TTF molecule has maximum four coordination sites (S1, S2, S3, S4) m-1monodentate ligandtrans-bidentate ET-ligandcoordination sites of ETCu-S bond lengths/compound no.cis-bidentate ET-ligand2.37

    2.382.31

    2.30, 2.36 2.30, 2.31, 2.38, 2.42 2.27, 2.38S1tb-1tb-2cb-1cb-2cb-3S1 and S4S1 and S3S1 and S3 ?Typical CuI-S coordination bond distances: 2.31-2.42 New type-II compounds of BEDT-TTF

  • Construction of novel fused p-d systemIntegration of conductivity and magnetismDirect bonding between -conjugated molecules and transition metal ions is importantS atoms of ethylenedithio-base are able to coordinate directly to Cu ionsBEDT-TTF molecule is a ligand with maximum 4 coordination sitesUsing BEDT-TTF, construct fused -d system like (DMeDCNQI)2Cu

  • (1) (BEDT-TTF2+)Cu2Br4BEDT-TTF-CuBr single crystals by Kanahama et al.

    (2) (BEDT-TTF2+)2Cu6Br10(3) (BEDT-TTF)2[Cu4Br6 BEDT-TTF] (4) (BEDT-TTF)2Cu2Br4(5) (BEDT-TTF2+)2Cu3Br7(H2O)(6) (BEDT-TTF2+)2Cu6Br10(H2O)2 R. Kanehama, M. Umemiya, F. Iwahori, H. Miyasaka, K.-i. Sugiura, M. Yamashita, Y. Yokochi, H. Ito, S. Kuroda, H. Kishida, H. Okamoto, M. Kaneko, Inorg. Chem., 42 (2003) 7173-7181. Diffusing reaction between CuIIBr2 in methanol (9.010-2 M) and ET in THF (2.610-3 M)CuCuBrBrS-Cu :2.38c

  • BEDT-TTF molecules align differently on each chain0.03eV0.04eV0.08eV0.04eV0.03eVOne-dimentional chain made of BEDT-TTF and Cu2Br4, but larger interchain transfer integrals are found.a= 9.401 =98.48b=10.841 P21/nc=10.035 Z=2

  • (BEDT-TTF) Cu2Br4Valence state of Cu ionsNo signal from Cu2+Signal from BEDT-TTF is observed but (BEDT-TTF)2Cu2(CN)3 withCu2+ ions (Tc=4K SC)T. Komatsu et alJ. Phys. Soc. Jpn. 65, 1340 (1996)2.0140 aligned crystals

  • (BEDT-TTF) Cu2Br4From X-ray structure analysisCentral C=C bond1.42(1)BEDT-TTF moleculesare divalentL. K. Chou et al., Chem. Mater. 7, 530 (1995)Former divalent ET salts(ET) (ClO4)2 (ET) (BF4)2(ET) [Fe(CN)4(CO)2]1993 Abboud et al.1995 Chou et al.2004 X. Xiao et al.All are insulating with conductivity less than 10-5 S/cm

    valenceC=CET01.312(ET)2ClO4(TCE)0.51/21.359(ET)3ClO22/31.366-(ET) ClO411.390(ET) (ClO4)221.439

  • (BEDT-TTF) Cu2Br4 Raman shift from BEDT-TTF2+962310H. H.Wang, A. M. Kini, J. M. Williams,Raman Characterization of the BEDT-TTF(ClO4)2 Salt Mol. Cryst. Liq. Cryst. 1996, 284, 211-221.

  • (BEDT-TTF) Cu2Br4What is charge carriers ?In spite that BEDT-TTF molecules are divalent,we observe considerable conductivity s=10-2 S/cm (at R.T.) HOMO2nd HOMO0+1+2What is the origin of carriers ?Electrons are removed from HOMO band !c axis resistivityanisotropy ratio //c / c=10-20

  • (BEDT-TTF) Cu2Br4 Hall effect at 300 K Ns=4.31020 /mol Hall effect at 300K1spin / 1.4103 moleculesCurie spin from BEDT-TTFC=2.710-4 emuK/mol
  • (BEDT-TTF)Cu2Br4 Temperature dependent carrier numberCarrier number increases with temperature to approaching ESR spin numberMeasurement on three different crystals.Ea=0.12eVEa=0.17eV~ 1cm2/VsHall mobility from =nemband conductionExtrinsic Semiconductor

  • 10(BEDT-TTF)Cu2Br4 BEDT-TTF ESR signal lineshapeLocalized spin at T< 100 K10all10Mobile spin at T > 100 KHESR tube40 alignedcrystalsg1=2.012g2=2.007H[110]ab

  • activation energy changes at 170 K

    Ea [eV]0 GPa0.45 GPa0.75 GPa1 GPaabove 170 K0.0890.0850.0720.065below 170 K0.1560.1440.1250.118

  • (BEDT-TTF)Cu2Br4 ThermopowerFor interacting fermions with spin (density r) explains thermopower at high temperature Courtesy of U. Mizutani and T. TakamiNegative thermopower

    electronic carrier.heaterChaikin and Beni, Phys. Rev. B 13 (1976) 647

  • (BEDT-TTF)Cu2Br4 Band structure and carrier excitation2nd HOMO~0.17 eVtrap sitescalculated band by extended Hckel methodHOMOOptical band gap ~0.7 eV

  • Summary(BEDT-TTF)Cu2Br4 is made of divalent BEDT-TTF molecules.In spite of closed electronic structure, it exhibits electrical conductivity as high as 10-2 S/cm.

    Hall carrier density increases with temperature as Curie spins at low temperature start to move above 100 K. (BEDT-TTF)Cu2Br4 is understood as extrinsic semiconductor in whichelectronic carriers trapped at low temperature are excited to HOMO band to contribute conduction at high temperature.

    Trap sites per 1.4103 molecules may be non-stoichiometric defects, for example, mixing of coproduct phase of (BEDT-TTF)2[Cu4Br6 BEDT-TTF]

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