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Electronic effects in LaTiO3/LaAlO3 superlattices

Published online by Cambridge University Press:  12 July 2019

G.W.J. Hassink
Affiliation:
MESA + Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
N. Nakagawa
Affiliation:
Department of Advanced Materials Science, University of Tokyo, Kashiwa, Chiba 277-8561, Japan
M. Takizawa
Affiliation:
Department of Complexity Science and Engineering, University of Tokyo, Kashiwa, Chiba 277-8561, Japan
H. Wadati
Affiliation:
Department of Complexity Science and Engineering, University of Tokyo, Kashiwa, Chiba 277-8561, Japan
L. Fitting Kourkoutis
Affiliation:
School of Applied and Engineering Physics, Cornell University, Ithaca, NY 14853, U.S.A.
S.S.E. Soe
Affiliation:
ReCOE, Seoul National University, Seoul 151-747, Korea
Y. Takata
Affiliation:
ReCOE, Seoul National University, Seoul 151-747, Korea
K. Horiba
Affiliation:
SPring-8/RIKEN, Mikazuki, Hyogo 679-5148, Japan
M. Matsunami
Affiliation:
SPring-8/RIKEN, Mikazuki, Hyogo 679-5148, Japan
S. Shin
Affiliation:
SPring-8/RIKEN, Mikazuki, Hyogo 679-5148, Japan
M. Yabashi
Affiliation:
SPring-8/RIKEN, Mikazuki, Hyogo 679-5148, Japan SPring-8/JASRI, Mikazuki, Hyogo 679-5198, Japan
K. Tamasaku
Affiliation:
SPring-8/RIKEN, Mikazuki, Hyogo 679-5148, Japan
Y. Nishino
Affiliation:
SPring-8/RIKEN, Mikazuki, Hyogo 679-5148, Japan
D. Miwa
Affiliation:
SPring-8/RIKEN, Mikazuki, Hyogo 679-5148, Japan
T. Ishikawa
Affiliation:
SPring-8/RIKEN, Mikazuki, Hyogo 679-5148, Japan SPring-8/JASRI, Mikazuki, Hyogo 679-5198, Japan
T. Susaki
Affiliation:
Department of Advanced Materials Science, University of Tokyo, Kashiwa, Chiba 277-8561, Japan
G. Rijnders
Affiliation:
MESA + Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
T.W. Noh
Affiliation:
ReCOE, Seoul National University, Seoul 151-747, Korea
D.A. Muller
Affiliation:
School of Applied and Engineering Physics, Cornell University, Ithaca, NY 14853, U.S.A.
A. Fujimori
Affiliation:
Department of Complexity Science and Engineering, University of Tokyo, Kashiwa, Chiba 277-8561, Japan
H.Y. Hwang
Affiliation:
Department of Advanced Materials Science, University of Tokyo, Kashiwa, Chiba 277-8561, Japan
D.H.A. Blank
Affiliation:
MESA + Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
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Abstract

Format

This is a copy of the slides presented at the meeting but not formally written up for the volume.

Abstract

Description: Semiconductor physics contains a rich body of theory and working designs. However, their material properties seem to be reaching their limits. Perovskite oxides on the other hand have abundant physical properties, but are still under active investigation. The advent of RHEED-monitoring of pulsed laser deposition allows for the fabrication of structures with single unit cell (4 Å) thick layers. In this way we may be able to fabricate quantum well structures for both applications and fundamental investigations. Superlattices of the Mott insulator LaTiO3 (LTO) and the band gap insulator SrTiO3 (STO) form such a structure. The superlattices are metallic, both as-grown and post-annealed [1]. This has been attributed to the existence of metallic states at the interfaces between LTO and STO [2]. At these interfaces the electron density is found to extend about 10 Å into the STO. However, theoretically, the required length scale for quantum confinement is of the order of 4 Å. A possible way to increase this confinement is to use a buffer material with a larger band gap than that of LTO (similar to semiconductor band gap engineering) and/or with a lower dielectric constant [2]. LaAlO3 (LAO) is such a material (ΔELAO = 5.6 eV vs. ΔESTO = 3.2 eV, εLAO = 24 vs. εSTO = 300). Here we report on the growth of LTO/LAO superlattices on STO substrates. As-grown superlattices of LTO/LAO are metallic, while post-annealing turns them insulating. This may be explained from a disorder-order transition in a 2D Mott-Hubbard model [3]. XPS and EELS measurements of the titanium valence show interesting differences for LTO layers close to and far away from the sample surface. The former, for thin LAO capping layers, show the presence of Ti4+ while the latter only have Ti3+. Hard XPS of samples with varying capping layer thickness shows an exponential dependence of the Ti3+ contents on a length scale of about 5 unit cells. [1] A. Ohtomo et al., Nature 419, 378-380 (2002). [2] S. Okamoto & A.J. Millis, Phys. Rev. B 70, 075101 (2004). [3] D. Heidarian & N. Trivedi, Phys. Rev. Lett. 93, 126401 (2004).

Type
Slide Presentations
Copyright
Copyright © Materials Research Society 2007

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