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5th Windsor Summer School Quantum Phenomena in Low-Dimensional Materials and Nanostructures, Cumberland Lodge, Windsor, UK, August 9 - 21, 2010
Heterostructures of transitionHeterostructures of transition--metal oxidesmetal oxides-- Experiment, mainly spectroscopy Experiment, mainly spectroscopy --
Atsushi FujimoriUniversity of Tokyo
-
New opportunities with oxide thin filmsNew opportunities with oxide thin films
Finite thicknessEpitaxial strain
Interfaces
substratee.g., SrTiO3
-
OutlineOutline
Electronic structure of transition-metal oxides
Fabrication and characterization
Interfacial electronic structure Effects of finite thickness Effects of epitaxial strain
-
Electronic structure of transition-metal oxides
-
MetalMetal--insulator transition through collapse insulator transition through collapse of Mott gap of Mott gap Bandwidth controlBandwidth control
U
U > W U < W
O 2p
3d
3d
U
W
W
Gap ~ U - W
O 2p
3d
3d
W
W
-
MetalMetal--insulator transition through carrier insulator transition through carrier doping into Mott insulator doping into Mott insulator Filling controlFilling control
n = 1 n < 1 (>1)
O 2p
3d
3d
U
W
W
Gap ~ U - W
O 2p
3d
3d
U
W
W
-
BandwidthBandwidth-- versusversus fillingfilling--controlled controlled metalmetal--insulator transitioninsulator transition
BA
ND
WID
TH
n1
U/W
or/
W
Filling-controlled MIT
Bandwidth-controlled MIT
M. Imada, A. Fujimori and Y. Tokura, Rev. Mod. Phys. 1998
U/W or /W ~ 1
-
3d
3d
UW
W
W
UW
W
W*
W
W
U U
W
W
gap ~ U - W
Brinkman-Rice picture
Hubbard picture
m* 1/W* Normal metal
U / W 1 U/W
-
X.Y. Zhang et al., Phys. Rev. Lett., 1993
U / W
-
Filling control
Ban
dwid
th c
ontro
l
BandwidthBandwidth-- versusversus fillingfilling--controlled controlled in Mottin Mott--Hubbard systemsHubbard systems
4+
4+
4+
3+
3+
3+3+
4+
4+
W cos2
Perovskite structure
-
U
W
U / W
-
Filling control
Ban
dwid
th c
ontro
l
BandwidthBandwidth-- versusversus fillingfilling--controlled controlled in Mottin Mott--Hubbard systemsHubbard systems
4+
4+
4+
3+
3+
3+3+
4+
4+
W cos2
Perovskite structure
-
Y. Tokura et al. PRL 93
FillingFilling--controlled Mottcontrolled Mott--Hubbard system Hubbard system LaLa11--xxSrSrxxTiOTiO33
LaTiO3d1 Mott insulator
rigid band model
Kodowaki-Woods relationship
SrTiO3d0
1 0
1 0.8 0.6 0.4 0.2 0
x =0.2x =0.1
x =0
x =0.05
x =0.3
0.5
x
x
Wilson ratio: / ~ 2
n=1/RH~1-x
x 01
Electronic specific heat &Pauli-paramagnetic suseptibiulity
-
Filling control
Ban
dwid
th c
ontro
l
M. Imada, A. Fujimori and Y. Tokura, Rev. Mod. Phys. 98
PerovskitePerovskite--type transitiontype transition--metal metal oxdiesoxdies
-
ZaanenZaanen--SawatzkySawatzky--Allen diagramAllen diagram
J. Zaanen, G.A. Sawatzky and J.W. Allen, PRL 85
p-band metal
d-band metal
Charge-transfer type insulator
Mott-Hubbard type insulator
Negative-insulator
(eV)
~ U
~
0
-
> W < W
Gap ~ - W
O 2p
3d
3d
U O 2p3d
3d U
MetalMetal--insulator transition through collapse insulator transition through collapse of chargeof charge--transfer gap transfer gap Bandwidth controlBandwidth control
-
Gap ~ - W
O 2p
3d
3d
U
n = 1 n < 1
O 2p
3d
3d
U
MetalMetal--insulator transition through carrier insulator transition through carrier doping into chargedoping into charge--transfer insulatortransfer insulator
-
Filling control
Ban
dwid
th c
ontro
l
M. Imada, A. Fujimori and Y. Tokura, Rev. Mod. Phys. 98
PerovskitePerovskite--type transitiontype transition--metal metal oxdiesoxdies
Giant Magnetoresistance
Mn
Textbook Fermi liquidMott transition
TiV
Giant thermoelectricity
Co
A2BO4High-Tc
superconductivity
CuLa1-xSrxMnO3
-
Y. Tokura
Electronic structure of Mn ion
high-spin state
3
PerovskitePerovskite--type type MnMn oxdiesoxdies
orbital
octahedron
Hund coupling Cryst. fieldIf
Strongly hybridized withStrongly hybridized withO 2O 2pp orbitalsorbitals
-
JHHund coupling constant
spintspineS
gi
gi
2
r
rspin
spin
10Dq
eg
t2g
Double exchange model for magnetoDouble exchange model for magneto--resistance in resistance in MnMn oxdiesoxdies
-
La1-xSrxMnO3
La1-xSrxMnO3
Y. Tokura et al., J. Phys. Soc. Jpn. 94
Tc
Colossal magnetoresistance of Colossal magnetoresistance of MnMn oxdiesoxdiesR
esis
tivity
(cm
)
Temperature (K) Magnetic field (T)
Res
istiv
ity (
cm)
-
Filling control
Ban
dwid
th c
ontro
l
M. Imada, A. Fujimori and Y. Tokura, Rev. Mod. Phys. 98
PerovskitePerovskite--type transitiontype transition--metal metal oxdiesoxdies
Giant Magnetoresistance
Mn
Textbook Fermi liquidMott transition
Ti
Giant thermoelectricity
Co
A2BO4High-Tc
superconductivity
CuLa1-xSrxMnO3
Pr1-xCaxMnO3
-
S.Mori et al., Nature 98
Jahn-Teller distortion of MnO6 octahedron
Mn3+Mn4+
x=0.5 x=0.67
d3z2-r2
dx2-y2
Pr1-xCaxMnO3
SpinSpin--chargecharge--orbital ordering in perovskiteorbital ordering in perovskite--type type MnMn oxdiesoxdies
-
Y. Tomioka et al., Phys. Rev. B 1996 A. Asamitsu et al., Nature 1997
Magneto-resistance Resistance drop by electric field
Metal-insulator transition induced by H or E
Even bigger magnetoresistance in Even bigger magnetoresistance in narrownarrow--band band MnMn oxdiesoxdies
-
Fabrication and characterization
-
T. Ohnishi et al., APL 01.
Monitoring RHEED oscillations
MBE using pulsed laser deposition (PLD) MBE using pulsed laser deposition (PLD)
sintered polycrystalline
targets
Excime
r laser
RHEEDbeam Single crystal
substrate
Movingedge
Maskpattern
Laser heating
PLD system
-
Bulk SrVO3: a = 3.84 K. Yoshimatsu et al.
Characterization of epitaxially grown thin Characterization of epitaxially grown thin film on SrTiOfilm on SrTiO33(001) substrate(001) substrate
SrVO3 filma = 3.905 (= SrTiO3)c = 3.82
Tensile strain
Reciprocal space mappingof XRD pattern
Atomic force microscope(AFM)
Transmission electron Microscopy (TEM)
-
X-ray reflection
Characterization of epitaxially grown Characterization of epitaxially grown superlatticesuperlattice on SrTiOon SrTiO33(001) substrate(001) substrate
S.J. May et al. PRB 08
(001)
(002)
(003)
[(LaMnO3)11.8 / (SrMnO3)4.4]6 superlatticeTEM image
superspots
-
S(003) = 2fint - fLMO - fSMO
(003) (in units of 1/m+m): visible only at O 1s edge
O 2p hole doping only at interface.
S. Smadici et al.,. PRL 07
Soft X-ray scattering
Soft xSoft x--ray scattering from ray scattering from [(LaMnO[(LaMnO33))mm/(SrMnO/(SrMnO33))mm]]nn superlatticesuperlattice
X-ray scattering (reflectivity)
S.J. May et al. PRB 08
(001)
(002)
(003)
superspots
Small angle scatt. part
-
AFM image
LEED
Synchrotron radiation
Combinatorial Laser MBE Chamber
PhotoemissionChamber
PreparationChamber
Sample Entry
K. Horiba et al., Rev. Sci. Instrum. 74, 3406 (2003).
Combined photoemission-laser MBE systemOshima-Kumigashira group
400 nm
Photon Factory BL-1c, BL2c, BL-28
InIn--situsitu ARPES measurement system of ARPES measurement system of PLDPLD--grown oxide thin films grown oxide thin films
-
Photoemission spectroscopy of buried Photoemission spectroscopy of buried interfacesinterfaces
interface
Sensitivity M
ean
free
path
()
Kinetic energy (eV)Soft
x-raysHardx-raysVUV
UV
Probing depth of photoelectrons
~ 1 uc
Dep
th
1-2 uc
-
Photoemission spectroscopy of buried Photoemission spectroscopy of buried interfacesinterfaces
n-type band insulator SrTiO3, LaAlO3, TiO2, ZnO, etc
Mott insulator, metal, superconductor, etc
interfacial states
10.0 5.0 0Binding Energy (eV)
SrTiO3
O 2p
Sensitivity
2-3 uc
Dep
th
1-2 uc
-
Photoemission spectroscopy of buried Photoemission spectroscopy of buried interfacesinterfaces
5-10 uc
Mea
n fre
e pa
th (
)
Kinetic energy (eV)Soft
x-raysHardx-raysVUV
UV
~ 1 uc
30-50 ucsubstrate
V oxides
Sensitivity
Dep
th
interfacial stateson V oxide side
Probing depth of photoelectrons
-
Photoemission spectroscopy of buried Photoemission spectroscopy of buried interfacesinterfaces
Dep
th
5-10 uc
Mea
n fre
e pa
th (
)
Kinetic energy (eV)Soft
x-raysHardx-raysVUV
UV
~ 1 uc
30-50 ucsubstrate
interfacial statesV oxides
e
Inte
rface
/bul
k
d
Sensitivity
Dep
th
M. Sing et al., PRL 09
Probing depth of photoelectrons
-
A1 - A2
Polarized soft xPolarized soft x--ray absorption spectroscopy ray absorption spectroscopy (XAS)(XAS)
element specific probe
spin sum rule
orbital sum ruleMn 2p
core level
Mn 3dvalence level
h
spin-orbit splitting
spin-orbit splitting
X
Magnetic circular x-ray dichroism(XMCD)
-
X
XMCD of buried interfacesXMCD of buried interfaces
Non-magnetic (Induced magnetism)
Non-magnetic or Magnetic
ferromagnetic interface
element specific probe
XAS
XMCD
-
OutlineOutline
Electronic structure of transition-metal oxides
Fabrication and characterization
Interfacial electronic structure Effects of finite thickness Effects of epitaxial strain
-
Interfacial electronic structureMetallic states between two insulators
-States near the Fermi level-
Interfaces
substratee.g., SrTiO3
-
SrTiO3
LaTiO3 Metallic interfaces !
Metallic behavior of interfaces between Metallic behavior of interfaces between Mott insulator and band insulatorMott insulator and band insulator
SrTiO3: d0 (Ti4+) band insulator
LaTiO3: d1 (Ti3+) Mott insulator
Perovskite-type oxides ABO3
Sr2+
Ti4+ (d0)
O2-
La2+
Ti3+ (d1)
O2-
-
A. Ohtomo et al., Nature 02
Ti3+
5 un
ite c
ells
LaTiOLaTiO33 layers embedded in SrTiOlayers embedded in SrTiO33: : Penetration of Ti 3Penetration of Ti 3dd electrons into SrTiOelectrons into SrTiO33
La 3d
Atomically resolved EELS
Ti 2p
Energy loss (eV)
Ti3+ Ti4+
Ti4+Ti3+
La
density
SrTiO3
SrTiO3
- - -- - -- -
- -LaTiO3 - - - - -
SrO0 layer
LaO+ layer
[Ti4+O2]0layer
[Ti3+O2]-layer
- - - -
LaTiO3: d1 (Ti3+) Mott insulatorSrTiO3: d0 (Ti4+) band insulator
-
Metallic transport of SrTiOMetallic transport of SrTiO33/LaTiO/LaTiO33superlatticessuperlattices
LSTO2
2uc
x ucSrTiO3
LaTiO3
LaTiO3 2uc
x ucSrTiO3
LaTiO3
Lattice constant
K. Shibuya, M. Lippmaa et al., JJAP 04
Electrical resistivity
T2
-
Inte
nsity
(arb
. uni
ts)
-10 -8 -6 -4 -2 0Energy relative to EF (eV)
h = 21.2 eV
SrTiO3/LaTiO3
200
(A)
(B)
(C)
(D)
O 2p
e-
band gap: ~3 eV
h
Photoemission spectra of SrTiOPhotoemission spectra of SrTiO33/LaTiO/LaTiO33interfacesinterfaces
(SrO)0 layer
TiO2 layer
(LaO)1+ layer
SrTiO3
LaTiO3
SrTiO3
LaTiO3
SrTiO3
SrTiO3
LaTiO3
V 3d
M. Takizawa et al., PRL 06
incoherentcoherent
La/Srinterdiffusion
-
Ti 2p-3d resonant photoemission
e-h
SrTiO3
LaTiO3
SrTiO3
LaTiO3
SrTiO3
LaTiO3Inte
nsity
(arb
. uni
ts)
-2.0 -1.0 0Energy relative to EF (eV)
SrTiO3/LaTiO3on resonance(h = 466 eV)off resonance(h = 600 eV)
(A)
(B)
(C)
coherentincoherent
Photoemission spectra of SrTiOPhotoemission spectra of SrTiO33/LaTiO/LaTiO33interfacesinterfaces
(SrO)0 layer
TiO2 layer
(LaO)1+ layer
M. Takizawa et al., PRL 06
La/Srinterdiffusion
-
SrTiO3
LaTiO3
V(z) V(z)
Metallic
Ti3+ Ti3.5+
(SrO)0
(SrO)0
(SrO)0
(SrO)0
(SrO)0
(TiO2)0
(TiO2)0
(TiO2)0
(TiO2)0
(TiO2)0
(TiO2)0(LaO)+
(LaO)+
(LaO)+
(LaO)+
(LaO)+
(LaO)+
(TiO2)-
(TiO2)-
(TiO2)-
(TiO2)-
(TiO2)-
e/2
Metallicity at SrTiOMetallicity at SrTiO33/LaTiO/LaTiO3 3 interfaces resulting interfaces resulting from electronic reconstructionfrom electronic reconstruction
S. Okamoto and A. J. Millis, Nature 04, PRB 04
coherentincoherent
Empty d band
LHB UHB
Electronicreconstruction
Layer DMFT calculation including long-range Coulomb interaction
-
Interfacial electronic structure
Interfaces
substratee.g., SrTiO3
Metallic states between two insulators-Charge transfer in electronic reconstruction-
-
A. Ohtomo and H.Y. Hwang, Nature 04H.Y. Hwang, Science 07
High mobility of High mobility of nn--type carriers at interfaces type carriers at interfaces between two band insulatorsbetween two band insulators
+- e/2 Ti4+ Ti3.5+
Magneto-resistance
LaAlO3: band insulatorSrTiO3: band insulator
Metallic
Magneto-resistance
-
Critical thickness of ~4 Critical thickness of ~4 ucuc for conductivity for conductivity transition at LaAlOtransition at LaAlO33/SrTiO/SrTiO33 interfaceinterface
S. Thiel et al., Science 06 M. Huijben et al., Nature Mater.06
d
Insulating MetallicInsulating Metallic
~ 4 uc4 uc
-
Polar (111) surface of KPolar (111) surface of K33CC60 60 and its and its electronic reconstructionelectronic reconstruction
R. Hepster et al., PRB 00
1.5e1.5e
-
Photoemission spectroscopy of buried Photoemission spectroscopy of buried interfacesinterfaces
Binding Energy (eV)
O 1s core level
V 2p core level
V oxides
5-10 uc
interfaceinterfacial stateson V oxide side
Sensitivity
Dep
th
-
Evidence for TiEvidence for Ti3+3+ states at the states at the nn--type type LaAlOLaAlO33/SrTiO/SrTiO33 interfaceinterface
M. Sing et al., PRL 09
Ti3+ intensityTi 2p core-level spectra
-
1
x
6STO
n-type interfacep-type interface
Ti4+ Ti3+
~ 4 uc
LaAlO3(x uc)/SrTiO3
M. Takizawa et al.
LaAlOLaAlO33 overlayeroverlayer thickness dependence of Tithickness dependence of Ti3+3+concentration at LaAlOconcentration at LaAlO33/SrTiO/SrTiO33 interfaceinterface
Prepared at 10-5 Torr
Metallic
Insulating Ti4+ Ti4-+
-
A. Ohtomo and H.Y. Hwang, Nature 04; N. Nakagawa et al, Nat. Mater. 06H.Y. Hwang, Science 07
pp--type LaAlOtype LaAlO33/SrTiO/SrTiO33 interfaceinterface
+-
e/2
O/4
-
1
x
6STO
M. Takizawa et al.
Ti4+ Ti3+
LaAlO3(x uc)/SrTiO3
n-type interfacep-type interface
~ 4 uc ?
Prepared at 10-5 Torr
LaAlOLaAlO33 overlayeroverlayer thickness dependence of Tithickness dependence of Ti3+3+concentration at LaAlOconcentration at LaAlO33/SrTiO/SrTiO33 interfaceinterface
Ti4+ Ti4-+
-
Interfacial electronic structure
Interfaces
substratee.g., SrTiO3
Metallic states between two insulators-Potential change in electronic reconstruction-
-
Polar catastrophe model of LaAlOPolar catastrophe model of LaAlO33/SrTiO/SrTiO33
Y. Segal et al., PRB 09
SrTiO3 LaAlO3
/2
Energy shift?~1eV/uc
Critical thickness
-
M. Takizawa et al.
~0.1 eV/uc
Probing the potential slope in the LaAlOProbing the potential slope in the LaAlO33 layer layer of LaAlOof LaAlO33/SrTiO/SrTiO33
Al 2p Sr 3d relative core-level shifts
Same direction!
e-h e-
n-type p-type~1
eV/uc
-
Probing the potential slope in the LaAlOProbing the potential slope in the LaAlO33 layer layer of LaAlOof LaAlO33/SrTiO/SrTiO33
Y. Segal et al., PRB 09
La 3d5/2 Al 2p
La 3d and Al 2p core levels referenced to Sr 3d
~4 uc
~1 eV
/ucSr 3d La 4d relative
core-level shiftsPolar catastrophe model
~0.1 eV/uc
Opposite to the model!
n-type p-type
n-type p-type
-
A. Rizzi et al., JVSTB 99
GaN/SiC(0001)GaN/AlN(0001)
Probing the potential slope in Probing the potential slope in GaNGaN (0001) layers(0001) layers
~0.1 eV/nm ~0.1 eV/nm
substratesubstrate
in situ
differentsamples
overlayer overlayer
-
A. Rizzi et al., JVSTB 99
Calculated potential in polar GaN/SiC(0001)Calculated potential in polar GaN/SiC(0001)
Density of surface states
~0.3 eV/nm ~0.1 eV/nm
e/2
e/2
-
Short summaryShort summary-- Metallic states between two insulators Metallic states between two insulators --
Electronic reconstruction at insulator-insulator interfaces:
Charge transfer occurs as expected to avoid the polar catastroph, but the charge transfer starts well below the critical thickness of transport.
Potential slope as expected to avoid the polar catastrophe model is much reduced.
The above observations can be explained by the gradual reconstruction which starts well below the critical thickness.
-
Preparation dependence of carrier distributions at Preparation dependence of carrier distributions at the the nn--type LaAlOtype LaAlO33/SrTiO/SrTiO33 interfaceinterface
Cross-sectional AFM
O2-annealed
Prepared at 10-6 Torr
M. Basletic et al., Nat. Phys. 08M. Sing et al., PRL 09
Core-level photoemission
Prepared at 10-6 Torr O2-annealed
-
Novel physical properties of Novel physical properties of LaAlOLaAlO33/SrTiO/SrTiO33 interfacesinterfaces
Ferromagnetism
A. Brinkman et al. Nat. Mater. 07cf: MR by M B. Shalom et al., PRB 09N. Reyren et al. Science 07
Superconductivity
-
GateGate--voltage control of superconductivity at voltage control of superconductivity at LaAlOLaAlO33/SrTiO/SrTiO33 interfaceinterface
A.D. Caviglia et al., Nature 08
Resistivity for various gate voltages
-
GateGate--voltagevoltage--controlled LaAlOcontrolled LaAlO33/SrTiO/SrTiO33 interface:interface:Filling control or mobility control?Filling control or mobility control?
C. Bell et al., PRL 09
Resistivity for various gate voltages
Gate-voltage dependence of carrier density and mobility
-
Interfacial electronic structureFerromagnetism between non-magnetic materials
Interfaces
substratee.g., SrTiO3
-
T. Koida et al.,. PRB 02
Ferromagnetism in [(LaMnOFerromagnetism in [(LaMnO33))mm/(SrMnO/(SrMnO33))mm]]nnsuperlatticessuperlattices
Magnetization, resistivity
m=m
S.J. May et al.,. PRB 08
Polarized neutron reflectivity
TEM
[MnO2]0[LaO]+
[MnO2]-[SrO]0
-
S. Smadici et al.,. PRL 07H. Wadati
STEM image Temperature dependence
(003) resonance
Metallic behavior
Soft xSoft x--ray scattering from ray scattering from [(LaMnO[(LaMnO33))88/(SrMnO/(SrMnO33))44]]77/SrTiO/SrTiO33(001)(001)
-
Ferromagnetism in AF insulatorFerromagnetism in AF insulator--paramagnetic paramagnetic metal interfacesmetal interfaces
S. Takahashi et al., APL 01
CaMnO3: AF insulatorCaRuO3 : PM metal Magnetization and Tc
Magnetization
-
1.2
0.8
0.4
0.0Mom
ent
(B
/ M
n-at
om)
Mn orbital momet spin moment
CaMn1-xRuxO3
-1.2
-0.8
-0.4
0.0
Mom
ent
(B
/ R
u-at
om)
Ru
orbital moment spin moment
-0.2
0.0
0.2
Mom
ent
(B
/ f.
u.)
1.0 0.9 0.8 0.7 0.6 0.5Ru concentration x
XMCD SQUID
Mtotal
Mn 2Mn 2pp and Ru 3and Ru 3pp XMCD for XMCD for CaMnCaMn11--xxRuRuxxOO33 thin filmsthin films
K. Terai et al. PRB 08
XMCD spectra
Mn
Ru
Mn
Ru
total
spin
spin
orbital
orbital
Magnetic moments on Mn and Ru
CaRuO3 CaMn0.5Ru0.5O3
-
Ru (t2g)Mn (t2g, eg) Mn (t2g, eg)
EF
eg
t2g
eg
t2geg
t2g
eg
t2g
cf.) Double peroskite Sr2FeMoO6 D.D. Sarma et al., PRL 00, Z. Fang et al., PRB 01
hybridization
Mechanism for ferromagnetism in Mechanism for ferromagnetism in CaMnCaMn11--xxRuRuxxOO33 CaMnOCaMnO33/CaRuO/CaRuO33, too ?, too ?
itinerant
localizedexchange-split
localizedexchange-split
Eex
-
Interfacial electronic structureInterface between different ground states
Interfaces
substratee.g., SrTiO3
-
Interface between superconductor YBaInterface between superconductor YBa22CuCu33OO77and and ferromagnetferromagnet La,Ca)MnOLa,Ca)MnO33
J. Chakhalian et al., Nat. Phys. 06
XMCD of Cu and Mn
Antiparallel magn. moment
-
Interface between superconductor YBaInterface between superconductor YBa22CuCu33OO77and and ferromagnetferromagnet La,Ca)MnOLa,Ca)MnO33
J. Chakhalian et al., Nat. Phys. 06
XMCD of Cu and Mn
Antiparallel magn. moment
-
Interfacial electronic structureChemical potential
Interfaces
substratee.g., SrTiO3
-
T. Fujii et al., APL 05
To deduce chemical potential from To deduce chemical potential from II--VV characteristics of junctioncharacteristics of junction
EvacA B
A B
Schottky barrier height = A - B = B A(or built-in potential in p-n junction)
metal n-type semicond.
I-V characteristics of SrRuO3/SrTiO3
-
A. Sawa et al., APL 07
Chemical potential shift from the built-in potential of La1-xSrxMO3/SrTiO3 p-n (Schottky) junction
To deduce chemical potential shift from To deduce chemical potential shift from II--VV characteristics of junctioncharacteristics of junction
-
A. Fujimori et al., J. Electron Spectrosc. 02
Chemical potential shift from core-level XPS
To deduce chemical potential shift from To deduce chemical potential shift from II--VV characteristics of junctioncharacteristics of junction
A. Sawa et al., APL 07
Chemical potential shift from the built-in potential
-
Magnetic fieldMagnetic field--induced chemical potential shift induced chemical potential shift in Lain La2/32/3SrSr1/31/3MnOMnO33/organic conductor junction/organic conductor junction
D. Wu et al., PRL 05
1-x
x
eg1
eg2
Double exchange in Jahn-Teller-split eg band
JT
H
-
EkinEvac
Photoemissionspectrum
core level
valence bandE
h
h
h
To deduce chemical potential shift from To deduce chemical potential shift from corecore--level photoemissionlevel photoemission
work functionvacuum level
chemical potential+
Density of states (DOS)
Photoelectron count
kinetic energy
E E -
Energy referenceof spectrometerEF
EF
-
S. Yunoki et al., PRB, 2007
Carrier doping utilizing chemical potential Carrier doping utilizing chemical potential differencesdifferences
Manganite Cuprate
x ~ 0.15
x ~ 0
x ~ 0.4
x ~ 0
Superconducting
LSCO
-
Effects of finite thickness
Finite thickness
substratee.g., SrTiO3
Metal-insulator transitions
-
MetalMetal--toto--insulator transition in SrVOinsulator transition in SrVO33with decreasing film thickness ofwith decreasing film thickness of
K. Yoshimatsu et al., PRL 10, Orbital ordering? (P. Mahadevan)
DMFT calc
LHBMottgap
-
Small W large U/W ?
MetalMetal--toto--insulator transition in Srinsulator transition in SrRRuOuO33with decreasing film thickness ofwith decreasing film thickness of
P. Mahadevan et al., PRB 09D. Toyota et al., APL 05
Orbital-ordering AFMI ?
-
OutlineOutline
Electronic structure of transition-metal oxides
Fabrication and characterization
Interfacial electronic structure Effects of finite thickness Effects of epitaxial strain
-
Effects of epitaxial strainSuperconductivity
Epitaxial strain
e.g., SrTiO3
-
Tight-binding model
M. Abrecht et al., PRL 91
Bulk a = 3.784c =13.23, dAP = 2.43
Thin filma = 3.754(= SrLaAlO4)c = 13.29, dAP = 2.50
t = 0.145 eVt = 0.135 eV
Strained filmBulkLa2-xSrxCuO4/SrLaAlO4(001)
Band structure of LaBand structure of La22--xxSrSrxxCuOCuO44 (x=0.15) (x=0.15) under compressive strain studied by ARPESunder compressive strain studied by ARPES
-
Fermi surface of LaFermi surface of La22--xxSrSrxxCuOCuO44 (x=0.15) under (x=0.15) under compressive strain studied by ARPEScompressive strain studied by ARPES
t = 0.145 eV, t = 0.0052 eV
TTc c = 24K= 24K TTc c = 40K= 40K
Bulk Strained film
t = 0.135 eV, t = 0.036 eV
Tight-binding modelM. Abrecht et al., PRL 91
cf: Tensile strain: La2-xSrxCuO4/SrTiO3(001)D. Coleta et al., PRB 06
Large t Small t
-
E. Pavarini et al., PRL 01
t
t
t
Tc,max vs |t/t|
Empirical correlation between Empirical correlation between TTc c ,max,max and and nextnext--nearestnearest--neighbor hoppingneighbor hopping tt
|t/t|
D. Feng et al., PRL 01
ABBB
AB BB
bilayer cuprates
-
Effects of epitaxial strainMetal-insulator transitions
Epitaxial strain
e.g., SrTiO3
-
Electronic phase diagram of Electronic phase diagram of RR11--xxAAxxMnOMnO33
Y. Tokura and Y. Tomioka, JMMM 99
bandwidth (W)large small
W cos2
La1-xSrxMnO3
Pr1-xCaxMnO3Nd1-xSrxMnO3
Hole doping x Hole doping x Hole doping x
x = 0.5
-
Y. Konishi et al., JPSJ 99
compressive
tensile
Electronic phase diagram ofElectronic phase diagram ofLaLa11--xxSrSrxxMnOMnO33 under epitaxial strainunder epitaxial strain
FM
FM
C-AFI
C-AFI
A-AFM
A-AFM
-
HXHX--PES spectra of LaPES spectra of La11--xxSrSrxxMnOMnO33 (x=0.4) (x=0.4) under epitaxial strainunder epitaxial strain
K. Horiba et al., PRB 09
h=5.95 keV
-
Y. Konishi et al., JPSJ 99
compressive
tensile
Electronic phase diagram ofElectronic phase diagram ofLaLa11--xxSrSrxxMnOMnO33 under epitaxial strainunder epitaxial strain
FM
FM
C-AFI
C-AFI
A-AFM
A-AFM
-
K. Horiba et al., PRB 09
HXHX--PES spectra of LaPES spectra of La11--xxSrSrxxMnOMnO33 (x=0.5) (x=0.5) under epitaxial strainunder epitaxial strain
h=5.95 keV
-
Summary Summary
Electronic structure of transition-metal oxides Fabrication and characterization Interfacial electronic structure
Metallic states between two insulators States near the Fermi level Charge transfer in electronic reconstruction Potential change in electronic reconstruction
Ferromagnetism between non-magnetic materials Interface between different ground states Chemical potential
Effects of finite thickness Metal-insulator transitions
Effects of epitaxial strain Metal-insulator transitions Madelung potential shifts Changes in chemical potential shift
-
Acknowledgement Acknowledgement
VUV, soft x-ray photoemissionM. Takizawa, H. Wadati, M. Takizawa, T. Yoshida, K. Maekawa (U of Tokyo)H. Kumigashira, K. Horiba, K. Yoshimatsu, T. Okabe, M. Oshima, A. Maniwa, M. Minohara (U of Tokyo)Hard x-ray photoemissionS. Shin, Y. Takata, K. Horiba, M. Matsunami, M. Yabashi, K. Tamasaku, Y. Nishino, D. Miwa, T. Isikawa (SPring-8, RIKEN)E. Ikenaga, K. Kobayashi (JASRI)Materials synthesisH.Y. Hwang, Y. Hotta, S. Tsuda, T. Higuchi, T. Susaki (U of Tokyo)M. Lippmaa, K. Shibuya, N. Mihara (ISSP)M. Kawasaki (Tohoku U), H. Koinuma (U Tokyo, JST)Y. Muraoka (Okayama U), Z. Hiroi (ISSP)
Supported by: a Grant-in-Aid for Scientific Research, JSPS & Quantum Beam Technology Development Program, JST
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