Two Dimensional Electron Gases at Oxide Interfaces Jochen Mannhart - PowerPoint PPT Presentation

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. Caviglia R. Jany S. Gariglio T. Kopp D. Jaccard C. Richter J.-M. Triscone C.W. Schneider University of Geneva S. Thiel L. Fitting-Kourkoutis Augsburg University D. Muller D.G. Schlom Cornell University M. Warusawithana C. Cen Penn State University J. Levy University of Pittsburgh DFG: SFB 484, EC: Nanoxide

2-DEGs Can Be Realized in Oxides a Mg x Zn 1- x O P SP P PE [0001] 2DEG P SP ZnO substrate b 2.0 7 v = 4 T = 0.5 K x = 0.05, n = 9 � 10 11 cm –2 6 m = 14,000 cm 2 V –1 s –1 5 1.5 5 6 4 r xy (k Ω ) 7 r xx (k Ω ) 1.0 8 3 2 0.5 1 0 0.00 2 4 6 8 10 B (T) A. Tsukazaki et al. , Science (2007)

The n -type LaAlO 3 / SrTiO 3 Interface LaAlO 3 band-insulator … AlO 2 LaO LaTiO 3 TiO 2 SrO … SrTiO 3 band-insulator, quantum-paraelectric [001] A. Ohtomo, H. Hwang, Nature 427 , 423 (2004)

8 unit cells LaAlO 3 on SrTiO 3 10 4 R ☐ ( Ω ) Al La O 10 3 Ti Sr 10 2 10 100 T (K) σ s ( Ω / ☐ ) -1 n S (cm -2 ) µ (cm 2 /Vs) 300 K 5 × 10 -5 2-4 × 10 13 7 4.2 K 5 × 10 -3 2-4 × 10 13 700

STEM: Cross Section LAADF HAADF 5 uc LaAlO 3 [001] SrTiO 3 Substrate L. Fitting-Kourkoutis, D.A. Muller (Cornell)

The Polar Catastrophe is another Possible Source of Charge Carriers ρ ρ E V V 0.5+ - - AlO 2 AlO 2 1- 1- 1+ LaO + 1+ LaO + - - 1- AlO 2 1- AlO 2 1+ 1+ LaO + LaO + 0.5- 0 TiO 2 TiO 2 0 0 0 SrO 0 SrO 0 0 0 0 TiO 2 0 TiO 2 0 0 0 0 SrO 0 SrO 0 N. Nakagawa et al. , Nature Materials (2006) D 9

Patterning the Electron Gas PMMA 2 uc LaAlO 3 SrTiO 3 poly LaAlO 3 3 uc 2 uc LaAlO 3 q2-DEG SrTiO 3 interface is not exposed to environment surface remains unexposed compatible with standard lithography techniques Schneider et al. , APL 89 , 122101 (2006) D 10

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

Low Carrier Density at the Interfaces ~2-4 × 10 13 /cm 2 TiO 2 -plane Ti O 3.9 Å

Gate-Field Induced Phase Transition to 2-DEG? V G,f LaAlO 3 V G,f I S V S V D I D SrTiO 3 SrTiO 3 V G,b V G,b

Field Effect Experiments - Top Gate V G,top R s ( Ω ) I - LaAlO 3 : 5 unit cells V - 300 K V + I + + Au 30 nm poly-SrTiO 3 V G,top 5 uc LaAlO 3 V G (V) - SrTiO 3

Field Effect Tuning of the Interface Properties A.D. Caviglia et al. , nature 2008

Measured Phase Diagram of the LaAlO 3 /SrTiO 3 Interface ∝ ( V G - V Gc ) 2/3 T BKT weak localisation R 400 mK (k Ω / ⃞ ) T BKT (mK) V G (V) large n ~10 13 /cm 2 ~4.5 × 10 13 /cm 2 A.D. Caviglia et al. , nature 2008

Electric Field Lithography induce insulator-metal transition locally V tip 300 K conductance ( μ S) 3 2 D D 0 1 SrTiO 3 3 uc LaAlO 3 0 0 20 40 60 tip position ( μ m) 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)

Electric Field Lithography induce insulator-metal transition locally 1.5 0.4 (d I /d x ) -1 (A/m) 1.0 I (nA) δ x = 2.1 nm Wikipedia 0.2 0.5 written wires with nanotube diameter 0.0 0.0 -5 0 5 x (nm) 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)

Possible Writing Mechanism No vacancies Vacancy density n v =1/4 C. Cen et al., Science in press

2DEG subbands E C μ GaAs E V LaAlO 3 /SrTiO 3 (AlGa)As/GaAs Heterostructure