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Two Dimensional Electron Gases at Oxide Interfaces Jochen Mannhart Center for Electronic Correlations and Magnetism University of Augsburg JST-DFG Workshop on Nanoelectronics, Kyoto, Jan. 21, 2009 G. Hammerl N. Reyren A. Herrnberger A.D.

SLIDE 1

Two Dimensional Electron Gases at Oxide Interfaces Jochen Mannhart Center for Electronic Correlations and Magnetism University of Augsburg

JST-DFG Workshop on Nanoelectronics, Kyoto, Jan. 21, 2009

SLIDE 2

G. Hammerl
A. Herrnberger
R. Jany
T. Kopp
C. Richter

C.W. Schneider

S. Thiel

Augsburg University

N. Reyren

A.D. Caviglia

S. Gariglio
D. Jaccard

J.-M. Triscone University of Geneva DFG: SFB 484, EC: Nanoxide

L. Fitting-Kourkoutis
D. Muller

Cornell University D.G. Schlom

M. Warusawithana

Penn State University

C. Cen
J. Levy

University of Pittsburgh

SLIDE 3

2-DEGs Can Be Realized in Oxides

MgxZn1-xO ZnO substrate [0001] 2DEG PSP PPE PSP a 2.0 1.5 1.0 0.5 0.00 2 4 8 B (T) rxx (kΩ) rxy (kΩ) 7 6 5 v = 4 T = 0.5 K x = 0.05, n = 9 1011 cm–2 m = 14,000 cm2 V–1 s–1 6 8 10 1 2 3 4 5 6 7 b

A. Tsukazaki et al., Science (2007)

SLIDE 4

LaTiO3

The n-type LaAlO3 / SrTiO3 Interface

SrO TiO2 LaO AlO2 [001] … … LaAlO3 band-insulator SrTiO3 band-insulator, quantum-paraelectric

A. Ohtomo, H. Hwang, Nature 427, 423 (2004)

SLIDE 5

SLIDE 6

8 unit cells LaAlO3 on SrTiO3

T (K) R☐(Ω)

100 10 102 103 104

Sr Ti La Al O

σs (Ω/☐)-1 nS (cm-2) µ (cm2/Vs)

300 K 5×10-5 2-4×1013 7 4.2 K 5×10-3 2-4×1013 700

SLIDE 7

STEM: Cross Section

5 uc LaAlO3

SrTiO3 Substrate

[001]

HAADF LAADF

L. Fitting-Kourkoutis, D.A. Muller (Cornell)

SLIDE 8

SLIDE 9

N. Nakagawa et al., Nature Materials (2006)

1+ 1- 1+ 1-

ρ

SrO0 TiO2 LaO+ AlO2

LaO+

AlO2

SrO0

TiO2

V

E

1+ 1- 1+ 1-

ρ V

SrO0 TiO2 LaO+ AlO2

LaO+

AlO2

SrO0

TiO2

0.5+ 0.5-

The Polar Catastrophe is another Possible Source of Charge Carriers

SLIDE 10

Patterning the Electron Gas

interface is not exposed to environment surface remains unexposed compatible with standard lithography techniques

SrTiO3 2 uc LaAlO3 PMMA poly LaAlO3 SrTiO3 2 uc LaAlO3 q2-DEG 3 uc

Schneider et al., APL 89, 122101 (2006)

SLIDE 11

200 nm

Schneider et al., APL 89, 122101 (2006)

SLIDE 12

SLIDE 13

SLIDE 14

Low Carrier Density at the Interfaces ~2-4×1013/cm2 TiO2-plane

Ti O

3.9 Å

SLIDE 15

VG,b SrTiO3 LaAlO3 SrTiO3 VG,f VS IS VD ID VG,b VG,f

Gate-Field Induced Phase Transition to 2-DEG?

SLIDE 16

Field Effect Experiments - Top Gate

VG,top

SrTiO3 5 uc LaAlO3 30 nm poly-SrTiO3 Au

VG,top

I- I+ V- V+

VG (V)

LaAlO3: 5 unit cells

Rs (Ω)

300 K

SLIDE 17

Field Effect Tuning of the Interface Properties

A.D. Caviglia et al., nature 2008

SLIDE 18

Measured Phase Diagram of the LaAlO3/SrTiO3 Interface

VG (V)

weak localisation

large n

R400 mK (kΩ /⃞) TBKT (mK)

~1013 /cm2

TBKT ∝ (VG-VGc)2/3

~4.5×1013 /cm2

A.D. Caviglia et al., nature 2008

SLIDE 19

Electric Field Lithography

tip position (μm) 20 40 60 1 2 3 300 K conductance (μS)

3 uc LaAlO3 D D0

Vtip

SrTiO3

induce insulator-metal transition locally

Nanowires can be written and erased repeatedly are stable at 300 K for > 24 h (but not always)

C. Cen et al., Nature Materials 7, 298 (2008)

SLIDE 20

Electric Field Lithography

induce insulator-metal transition locally

Nanowires can be written and erased repeatedly are stable at 300 K for > 24 h (but not always)

(dI/dx)-1 (A/m)

I (nA)

0.0 0.5 1.0 1.5

x (nm)

5 0.0 0.2 0.4

δx = 2.1 nm

C. Cen et al., Nature Materials 7, 298 (2008)

written wires with nanotube diameter

Wikipedia

SLIDE 21

Possible Writing Mechanism

No vacancies Vacancy density nv=1/4

C. Cen et al., Science in press

SLIDE 22

SLIDE 23

Two Dimensional Electron Gases at Oxide Interfaces Jochen Mannhart Center for Electronic Correlations and Magnetism University of Augsburg

JST-DFG Workshop on Nanoelectronics, Kyoto, Jan. 21, 2009

C.W. Schneider

Augsburg University

A.D. Caviglia

J.-M. Triscone University of Geneva DFG: SFB 484, EC: Nanoxide

Cornell University D.G. Schlom

Penn State University

University of Pittsburgh

2-DEGs Can Be Realized in Oxides

LaTiO3

The n-type LaAlO3 / SrTiO3 Interface

SrO TiO2 LaO AlO2 [001] … … LaAlO3 band-insulator SrTiO3 band-insulator, quantum-paraelectric

8 unit cells LaAlO3 on SrTiO3

T (K) R☐(Ω)

σs (Ω/☐)-1 nS (cm-2) µ (cm2/Vs)

300 K 5×10-5 2-4×1013 7 4.2 K 5×10-3 2-4×1013 700

STEM: Cross Section

5 uc LaAlO3

HAADF LAADF

1+ 1- 1+ 1-

ρ

V

E

1+ 1- 1+ 1-

ρ V

0.5+ 0.5-

The Polar Catastrophe is another Possible Source of Charge Carriers

Patterning the Electron Gas

interface is not exposed to environment surface remains unexposed compatible with standard lithography techniques

SrTiO3 2 uc LaAlO3 PMMA poly LaAlO3 SrTiO3 2 uc LaAlO3 q2-DEG 3 uc

Schneider et al., APL 89, 122101 (2006)

200 nm

Schneider et al., APL 89, 122101 (2006)

Low Carrier Density at the Interfaces ~2-4×1013/cm2 TiO2-plane

Ti O

3.9 Å

VG,b SrTiO3 LaAlO3 SrTiO3 VG,f VS IS VD ID VG,b VG,f

Gate-Field Induced Phase Transition to 2-DEG?

Field Effect Experiments - Top Gate

VG,top

VG,top

I- I+ V- V+

VG (V)

Rs (Ω)

Field Effect Tuning of the Interface Properties

Measured Phase Diagram of the LaAlO3/SrTiO3 Interface

VG (V)

large n

R400 mK (kΩ /⃞) TBKT (mK)

~1013 /cm2

~4.5×1013 /cm2

Electric Field Lithography

induce insulator-metal transition locally

Nanowires can be written and erased repeatedly are stable at 300 K for > 24 h (but not always)

Electric Field Lithography

induce insulator-metal transition locally

Nanowires can be written and erased repeatedly are stable at 300 K for > 24 h (but not always)

(dI/dx)-1 (A/m)

I (nA)

0.0 0.5 1.0 1.5

x (nm)

5 0.0 0.2 0.4

written wires with nanotube diameter

Possible Writing Mechanism

No vacancies Vacancy density nv=1/4

LaAlO3/SrTiO3

GaAs μ 2DEG subbands EC EV

(AlGa)As/GaAs Heterostructure