物構研シンポ 澤 091117 R -...

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強相関酸化物ヘテロ界面の 相競合と新規物性 強相関酸化物ヘテロ界面の 強相関酸化物ヘテロ界面の 相競合と新規物性 相競合と新規物性 彰仁 1 ,山田 浩之 1 Ping-Hua Xiang 1,2 1 産業技術総合研究所 2 JST-CREST 彰仁 彰仁 1 1 ,山田 ,山田 浩之 浩之 1 1 Ping Ping - - Hua Xiang Hua Xiang 1,2 1,2 1 1 産業技術総合研究所 産業技術総合研究所 2 2 JST JST - - CREST CREST 物構研シンポジウム'09「放射光・中性子・ミュオンを用いた表面・ 界面科学の最前線」 エポカルつくば,20091117日~18

Transcript of 物構研シンポ 澤 091117 R -...

  • 強相関酸化物ヘテロ界面の相競合と新規物性

    強相関酸化物ヘテロ界面の強相関酸化物ヘテロ界面の相競合と新規物性相競合と新規物性

    澤 彰仁1,山田 浩之1,Ping-Hua Xiang 1,21産業技術総合研究所

    2JST-CREST

    澤澤 彰仁彰仁11,山田,山田 浩之浩之11,,PingPing--Hua XiangHua Xiang 1,21,2

    11産業技術総合研究所産業技術総合研究所22JSTJST--CRESTCREST

    物構研シンポジウム'09「放射光・中性子・ミュオンを用いた表面・ 界面科学の最前線」エポカルつくば,2009年11月17日~18日

  • 強相関遷移金属酸化物強相関遷移金属酸化物超伝導超伝導 強磁性強磁性

    (Nd,Ce)2CuO4 (La,Sr)MnO3 BiFeO3

    強誘電+反強磁性強誘電+反強磁性(マルチフェロイック)(マルチフェロイック)

    Wang et al., Science 299, 1719 (2003)

    0

    0.2

    0.4

    0.6

    0.8

    1

    1.2

    0 0.5 1 1.5 2

    MR

    rat

    io ρ

    (H)/

    ρ(0)

    Magnetic field [T]

    115K 125K 135K

    (Nd,Sm)1/2

    Sr1/2

    MnO3

    磁場制御 光制御電場制御

    4

    Time (μs)

    Res

    ista

    nce(

    Ω)

    ↑Laser pulse

    30K

    Light

    -20 0 20 40 60100101102

    103104105106107108109

    105

    106

    107

    108

    109

    1010

    0 200 400 600 800 1000

    Pr1-x

    CaxMnO

    3

    (x=0.3)R

    esis

    tanc

    e [Ω

    ]

    Applied voltage [V]

    T=20 K, μ0H=0 T

    Asamitsu et al., Nature 388, 50 (1997) Fiebig et al., Scinence 280, 1925 (1998)Tomioka et al.

  • 遷移金属酸化物界面の特異な電子状態遷移金属酸化物界面の特異な電子状態

    LaAlOLaAlO33--SrTiOSrTiO33 Interface (band insulators)Interface (band insulators)

    Polar catastrophePolar catastrophe

    Ohtomo and Hwang,Nature 427,423 (2004)

    Nakagawa et al.,Nature Mater. 5, 204 (2006)

    Thiel et al., Science 313,1942 (2006)

    Reyren et al., Science 317,1196 (2007)

    Brinkman et al., Nature Mater. 6, 493 (2007)

    twotwo--dimensional electron gas?dimensional electron gas?

  • 強相関酸化物界面の特異な電子状態強相関酸化物界面の特異な電子状態

    LaMnOLaMnO33--SrMnOSrMnO33 Interface (Mott insulators)Interface (Mott insulators)

    [(LMO)m/(SMO)m]n

    Koida et al., PRB 66, 144418 (2002)

    Salvador et al., APL 75, 2638 (1999)Yamada et al., APL 89, 052506 (2006)Bhattacharya et al., PRL 99, 196404 (2007)

    Short-PeriodUniform ValenceAlloy-like metal

    Long-PeriodNonuniform Valence

    Interface Ferro.

    Ferro Metal

    cAF

    Ferro

    AF

    Ferro

    Ferro

    SrM

    nO3

    LaM

    nO3LaMnO3

    SrMnO3

    LaMnO3

    SrMnO3

    Charge transfer at interfaces Charge transfer at interfaces

  • CantedA-AFI

    G-AFI

    LaMnOLaMnO33

    SrMnOSrMnO33

    MnLa Sr

    LaMnOLaMnO33 SrMnOSrMnO33

    Phase diagram of LaPhase diagram of La11--xxSrSrxxMnOMnO33

    Ferromagnetic metal

    Interface has a doping level intermediate Interface has a doping level intermediate between LMO and SMO?between LMO and SMO?

    (~0.5)(~0.5)

    Electronic reconstruction at LMOElectronic reconstruction at LMO--SMO interfaceSMO interface

    Urushibara et al., PRB (1994)Mn4+ (t2g3eg0)

    t2g

    eg

    Mn3+ (t2g3eg1)

    t2g

    eg

    Charge transferCharge transfer

  • H. Nakao (PF-KEK) et al., JPSJ 78, 024602 (2009)

    Resonant XResonant X--ray Scatteringray Scattering

    LMO 2uc+SMO2uc SL

    abruptuniform

    Valence modulation may be very small.Interface roughness changes interfacial electronic states

    Recent studyRecent study

    Intrinsic electronic states at LMOIntrinsic electronic states at LMO--SMO interface ??SMO interface ??

  • RH

    EED

    Int

    ensi

    ty

    8006004002000Time (sec.)

    LMO

    SMO

    (1) Substrate-choice (2) Improvement of Samples

    LSAT: lattice-matching

    STO:tensile-strain

    LSAT3.87Å

    (La,Sr)(Al,Ta)O3

    interface

    SrTiO33.905Å

    LaMnO3(LMO)

    SrMnO3(SMO)

    Characterization with XRD

    1μm

    RHEED Oscillation

    FeedbackFeedback

    Strategy for highStrategy for high--quality superlattice synthesisquality superlattice synthesis

  • Characterization with Synchrotron XRDCharacterization with Synchrotron XRD

    BL4c , Photon Factory, KEK, Tsukuba, 2009 (Prof. Nakao)

    Clear Laue Fringes

    perfect structure

    Bad superlattice

    Good superlattice

    RT• Sharp superlattice reflection • Laue Fringes until h=1.5

    Modulation in superstructure

    Good as films, but structural imperfection

  • Impact of Improvement on Properties Impact of Improvement on Properties

    Bad L2S2La0.5Sr0.5MnO3

    = Ferro Metal

    Good L2S2 = Insulator

    L4S4, L5S5= Ferro InsulatorM, 1/ρ, Tc

    Bad > Good

    Bad- Good = Extrinsic FM

    (interface rougness etc.)

  • LaMnO3

    InsulatorAlloy-like(Ferro. Metal)

    SrMnO3

    LaOMnO2

    MnO2

    SrO

    LaO

    MnO2SrO

    interface

    ×

    LaMnO3

    SrMnO3

    Under-dopedNearly 3+

    Over-dopedNearly 4+

    Mn Valence?

    ? Even in the short periodicity, electronic state is not uniform.

    ? Charge transfer alone cannot explain the properties.

    Additional mechanism?Additional mechanism?

    ShortShort--Period LMOPeriod LMO--SMO SLSMO SL

  • Good L2S2

    HH--Induced InsulatorInduced Insulator--toto--Metal Transition Metal Transition

    FM

    AFI

    Metallic for H >7T : strong coupling with spin/orbital degrees of freedom

    Alloy LSMO/LSAT

    No large MR effect:

    H//film Sr

  • 10-3

    10-2

    10-1

    100

    101

    102

    ρ (Ω

    cm)

    -10 -5 0 5 10Magnetic Field (T)

    -2

    -1

    0

    1

    2

    M (μ

    B/M

    n)

    T=10 K

    Hann1T

    3T7T9T

    Hann1T3T7T

    zfc

    Cr-doped Nd0.5Ca0.5MnO3

    T. Kimura et al., PRL 83 (1999)

    Magnetorelaxor

    History of H-applicationaffects Msat and MR effect.

    Phase Separation H-annealing effect

    L2S2: MagneticL2S2: Magnetic--Field DependenceField Dependence

    FM domain Short-range Orbital-Order (AFI)

    Hann

    Phase competition at LMOPhase competition at LMO--SMO interfaceSMO interface

  • oneone--electron bandwidthelectron bandwidth

    ==

    Phase diagram of perovskite MnPhase diagram of perovskite Mn--oxidesoxides

    bibi--critical point: phase competitioncritical point: phase competition

    Lattice distortion induces an electronic phase variationLattice distortion induces an electronic phase variation

    Tomioka and Tokura, PRB 70, 014432 (2004)

  • LMO 2uc < SMO 3uc

    LMO 3uc > SMO 2ucFerromagnetic metal(TC=240K, M

  • GroundGround--State Phase Diagram State Phase Diagram

    Long-Period

    2u.c

    .

    4u

    .c. Sr

    MnO

    3

    LaMnO3 layer 2u.c. 6u.c.

    FI

    Short-Period complicated ground-states

    L2S2

    L2S3

    L3S2 FM

    AFIL4S4

    L5S5

    bulk-like properties

    LMO

    M-I boundary Insulator (L2S2)Nearly-metal MetalH

    CMR

    Insulator

  • ElectronElectron--doped CaMnOdoped CaMnO33

    G-type AF InsulatorInsulator

    Caspi et al., PRB 69, 104402 (2004)Tomioka et al., unpublished

    MetalMetal--insulator transition with lightly electron dopinginsulator transition with lightly electron doping

    Mn4+ (t2g3eg0)

    t2g

    eg

    Ce4+

    CaCa11--xxCeCexxMnOMnO33

    cG-type AF MetalMetal

    C-type AF InsulatorInsulator

  • 0 50 100 150 200 250 30010-3

    10-2

    10-1

    100

    101

    102

    CMO

    0 T 5 T

    Temperature (K)

    Res

    istiv

    ity (Ω

    cm)

    0 50 100 150 200 250 30010-3

    10-2

    10-1

    100

    101

    102

    CCMO8

    0 T 5 T

    Temperature (K)

    Res

    istiv

    ity (Ω

    cm)

    0 50 100 150 200 250 30010-3

    10-2

    10-1

    0 T 3 T 5 T 9 T

    Res

    istiv

    ity (Ω

    cm)

    Temperature (K)

    CCMO5x=0 x=0.05 x=0.08

    Substrate: (100)-oriented

    Ca1-xCexMnO3 (CCMO): x = 0 – 0.08

    NAO: NdAlO3 (aa = 0.3751 nm= 0.3751 nm, +0.3%)

    aa (CCMO x=0.05) ~ 0.374 nm(CCMO x=0.05) ~ 0.374 nm 1 μm x 1 μm

    Xiang et al., APL 94, 062109 (2009)

  • KrF Laser

    e-

    RHEED

    NAO

    CaMnO3 Ca1-xCexMnO3(x=0.08)

    0 50 100 150 200 250 30010-3

    10-2

    10-1

    100

    101

    102

    CMO

    CCMO8 CMO CMO@5T CCMO8 CCMO8@5T

    Temperature (K)

    Res

    istiv

    ity (Ω

    cm)

  • [CMO([CMO(xx=0)=0)××mm/CMO(/CMO(xx=0) )=0) )××nn]]CC--AFIAFIGG--AFIAFI

    C-AFI

    G-AFI

    C-AFI

    G-AFI

    Competition of different spin structuresCompetition of different spin structuresat interfacesat interfaces

    Charge transfer +Charge transfer +

    Phase separation?Phase separation?

    +

    interface

  • まとめまとめ

    強相関酸化物ヘテロ界面強相関酸化物ヘテロ界面

    ・電荷移動 ・・・・ 限定的(?)キャリア濃度は界面でシャープに変化界面1ユニットセル程度の領域だけでキャリア濃度が変化

    ・電子相競合強相関電子系の効果

    ・・・・ 軌道(格子)、スピンの協調と競合

    界面電子相・新機能界面電子相・新機能

    今後今後

    ・界面の局所構造・電子状態(価数、スピン状態など)の詳細な評価シンクロトロンX線実験,透過電子顕微鏡観察

    ・界面電子相競合状態の外場(電場、光など)による制御 ・・・・ 機能化