Abstract

The breaking of symmetry across an oxide heterostructure causes the electronic orbitals to be reconstructed at the interface into energy states that are different from their bulk counterparts1. The detailed nature of the orbital reconstruction critically affects the spatial confinement and the physical properties of the electrons occupying the interfacial orbitals2,3,4. Using an example of two-dimensional electron liquids forming at LaAlO3/SrTiO3 interfaces5,6 with different crystal symmetry, we show that the selective orbital occupation and spatial quantum confinement of electrons can be resolved with subnanometre resolution using inline electron holography. For the standard (001) interface, the charge density map obtained by inline electron holography shows that the two-dimensional electron liquid is confined to the interface with narrow spatial extension (~1.0 ± 0.3 nm in the half width). On the other hand, the two-dimensional electron liquid formed at the (111) interface shows a much broader spatial extension (~3.3 ± 0.3 nm) with the maximum density located ~2.4 nm away from the interface, in excellent agreement with density functional theory calculations.

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Change history

  • 30 May 2018

    In the version of this Letter originally published, in two instances in Fig. 1 the layers in the cross-sectional view of the (001) interface were incorrectly labelled: in Fig. 1b SrO+ should have read SrO0; in Fig. 1c LaO+, AlO2, LaO+, TiO20, SrO+, TiO20 should have read LaO33–, Al3+, LaO33–, Ti4+, SrO34–, Ti4+. In Fig. 3c the upper-right equation read –σs = –e/2a2 but should have read –σs = e/2a2 and in Fig. 3f the lower-right equation read –σs = –e/2√3a2 but should have read σs = –e/2√3a2. These errors have now been corrected in the online version of the Letter.

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Acknowledgements

This work was supported by AFOSR Asian Office of Aerospace Research and Development (AOARD) under grant number FA2386-15-1-4046 (S.H.O. and C.B.E.) and AFOSR under grant number FA9550-15-1-0334 (C.B.E.). Research at SKKU was supported by the Creative Materials Discovery Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, the ICT and Future Planning (NRF-2015M3D1A1070672) (S.H.O.), an NRF grant funded by the Korean government (NRF-2015R1A2A2A01007904) (S.H.O.) and by the Ministryof Trade, Industry & Energy (MOTIE, Korea) under Industrial Technology Innovation Program (10080654) (S.H.O.). K.S. and S.-Y.C. acknowledge the support of the Fundamental Research of the Korean Institute of Materials Science (KIMS-PNK5260) and the Global Frontier Hybrid Interface Materials of the NRF funded by Korea Government (2013M3A6B1078872). Research at the University of Nebraska was supported by NSF MRSEC (grant no. DMR-420645). C.T.K. acknowledges support by the German Research Foundation (DFG grant KO 2911/12-1).

Author information

Affiliations

  1. Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang, Republic of Korea

    • Kyung Song
    • , Bumsu Park
    • , Ja Kyung Lee
    • , Si-Young Choi
    •  & Sang Ho Oh
  2. Materials Modeling and Characterization Department, Korea Institute of Materials Science (KIMS), Changwon, Republic of Korea

    • Kyung Song
    •  & Si-Young Choi
  3. Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, WI, USA

    • Sangwoo Ryu
    • , Hyungwoo Lee
    •  & Chang-Beom Eom
  4. Department of Physics and Astronomy & Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, NE, USA

    • Tula R. Paudel
    •  & Evgeny Y. Tsymbal
  5. Department of Physics, Humboldt University of Berlin, Berlin, Germany

    • Christoph T. Koch
  6. Department of Energy Science, Sungkyunkwan University (SKKU), Suwon, Republic of Korea

    • Bumsu Park
    • , Young-Min Kim
    •  & Sang Ho Oh
  7. Center for Integrated Nanostructure Physics, Institute for Basic Science (IBS), Suwon, Republic of Korea

    • Ja Kyung Lee
    •  & Young-Min Kim
  8. School of Materials Science and Engineering, Ulsan National Institute of Science and Engineering (UNIST), Ulsan, Republic of Korea

    • Jong Chan Kim
    •  & Hu Young Jeong
  9. UNIST Central Research Facilities (UCRF), Ulsan National Institute of Science and Engineering (UNIST), Ulsan, Republic of Korea

    • Hu Young Jeong
  10. Department of Physics, University of Wisconsin-Madison, Madison, WI, USA

    • Mark S. Rzchowski

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Contributions

S.H.O. and C.B.E. conceived the project and designed the experiments. K.S. prepared TEM samples by dimpling and Ar+ ion milling methods, performed TEM, STEM and inline electron holography works under the supervision of S.H.O at POSTECH. S.R. and H.L. prepared the LAO/STO samples and characterized the electrical properties. C.T.K. developed the inline holography reconstruction software and advised the data processing and interpretation of the inline electron holography results. S.-Y.C. contributed to the sample preparation, STEM and inline electron holography works at KIMS and developed the MATLAB-based software for measurement of the atomic displacements presented in Supplementary Fig. 5. J.K.L. and B.P. carried out supporting STEM HAADF imaging, STEM-EELS and STEM-EDS using STEM facilities at SKKU under the supervision of S.H.O. Y.-M.K. contributed to the STEM works at SKKU. T.R.P. and E.Y.T performed the DFT calculation. J.C.K. and H.Y.J. prepared TEM samples by using FIB, of which data are presented in Supplementary Information. M.S.R. supervised the electrical transport measurements. All authors analysed the data, discussed the results and contributed to the writing of the paper.

Corresponding author

Correspondence to Sang Ho Oh.

Supplementary information

  1. Supplementary Information

    Supplementary Figures 1–23, Supplementary Tables 1–3, Supplementary Text 1–7.

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DOI

https://doi.org/10.1038/s41565-017-0040-8