Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Direct imaging of the electron liquid at oxide interfaces

A Publisher Correction to this article was published on 30 May 2018

This article has been updated

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.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.

from$8.99

All prices are NET prices.

Fig. 1: Orientation-dependent energy subbands of Ti 3d orbitals and orbital-selective quantum confinement of 2DELs at LAO/STO interfaces.
Fig. 2: Conceptual representation of the electrostatic potential mapping by inline electron holography for 2DEL imaging.
Fig. 3: Internal electric fields measured by inline electron holography and models for electronic reconstruction of LAO/STO (001) and (111) heterostructures.
Fig. 4: Direct imaging of the 2DELs at oxide interfaces.

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.

References

  1. 1.

    Chakhalian, J. et al. Orbital reconstruction and covalent bonding at an oxide interface. Science 318, 1114–1117 (2007).

    Article  Google Scholar 

  2. 2.

    Okamoto, S. & Millis, A. J. Electronic reconstruction at an interface between a Mott insulator and a band insulator. Nature 428, 630–633 (2004).

    Article  Google Scholar 

  3. 3.

    Mannhart, J. & Schlom, D. G. Oxide interfaces—An opportunity for electronics. Science 327, 1607–1611 (2010).

    Article  Google Scholar 

  4. 4.

    Zubko, P. et al. Interface physics in complex oxide heterostructures. Annu. Rev. Condens. Matter Phys. 2, 141–165 (2011).

    Article  Google Scholar 

  5. 5.

    Ohtomo, A. & Hwang, H. A high-mobility electron gas at the LaAlO3/SrTiO3 heterointerface. Nature 427, 423–426 (2004).

    Article  Google Scholar 

  6. 6.

    Jang, H. W. et al. Metallic and insulating oxide interfaces controlled by electronic correlations. Science 331, 886–889 (2011).

    Article  Google Scholar 

  7. 7.

    Hwang, H. Y. et al. Emergent phenomena at oxide interfaces. Nat. Mater. 11, 103–113 (2012).

    Article  Google Scholar 

  8. 8.

    Breitschaft, M. et al. Two-dimensional electron liquid state at LaAlO3–SrTiO3 interfaces. Phys. Rev. B 81, 153414 (2010).

    Article  Google Scholar 

  9. 9.

    Salluzzo, M. et al. Orbital reconstruction and the two-dimensional electron gas at the LaAlO3/SrTiO3 interface. Phys. Rev. Lett. 102, 166804 (2009).

    Article  Google Scholar 

  10. 10.

    Delugas, P. et al. Spontaneous 2-dimensional carrier confinement at the n-type SrTiO3/LaAlO3 interface. Phys. Rev. Lett. 106, 166807 (2011).

    Article  Google Scholar 

  11. 11.

    Doennig, D., Pickett, W. E. & Pentcheva, R. Massive symmetry breaking in LaAlO3/SrTiO3 (111) quantum wells: A three-orbital strongly correlated generalization of graphene. Phys. Rev. Lett. 111, 126804 (2013).

    Article  Google Scholar 

  12. 12.

    Reyren, N. et al. Superconducting interfaces between insulating oxides. Science 317, 1196–1199 (2007).

    Article  Google Scholar 

  13. 13.

    Caviglia, A. et al. Tunable Rashba spin–orbit interaction at oxide interfaces. Phys. Rev. Lett. 104, 126803 (2010).

    Article  Google Scholar 

  14. 14.

    Brinkman, A. et al. Magnetic effects at the interface between non-magnetic oxides. Nat. Mater. 6, 493–496 (2007).

    Article  Google Scholar 

  15. 15.

    Pesquera, D. et al. Two-dimensional electron gases at LaAlO3/SrTiO3 interfaces: Orbital symmetry and hierarchy engineered by crystal orientation. Phys. Rev. Lett. 113, 156802 (2014).

    Article  Google Scholar 

  16. 16.

    McKeown Walker, S. et al. Control of a two-dimensional electron gas on SrTiO3(111) by atomic oxygen. Phys. Rev. Lett. 113, 177601 (2014).

    Article  Google Scholar 

  17. 17.

    Herranz, G. et al. Engineering two-dimensional superconductivity and Rashba spin–orbit coupling in LaAlO3/SrTiO3 quantum wells by selective orbital occupancy. Nat. Commun. 6, 6028 (2015).

    Article  Google Scholar 

  18. 18.

    Berner, G. et al. Direct k-space mapping of the electronic structure in an oxide–oxide interface. Phy. Rev. Lett. 110, 247601 (2013).

    Article  Google Scholar 

  19. 19.

    Basletic, M. et al. Mapping the spatial distribution of charge carriers in LaAlO3/SrTiO3 heterostructures. Nat. Mater. 7, 621–625 (2008).

    Article  Google Scholar 

  20. 20.

    Huang, B.-C. et al. Mapping band alignment across complex oxide heterointerfaces. Phys. Rev. Lett. 109, 246807 (2012).

    Article  Google Scholar 

  21. 21.

    Koch, C. T. & Lubk, A. Off-axis and inline electron holography: A quantitative comparison. Ultramicroscopy 110, 460–471 (2010).

    Article  Google Scholar 

  22. 22.

    Midgley, Pa & Dunin-Borkowski, R. E. Electron tomography and holography in materials science. Nat. Mater. 8, 271–280 (2009).

    Article  Google Scholar 

  23. 23.

    Pentcheva, R. & Pickett, W. E. Avoiding the polarization catastrophe in LaAlO3 overlayers on SrTiO3 (001) through polar distortion. Phys. Rev. Lett. 102, 107602 (2009).

    Article  Google Scholar 

  24. 24.

    Pauli, S. A. et al. Evolution of the interfacial structure of LaAlO3 on SrTiO3. Phys. Rev. Lett. 106, 036101 (2011).

    Article  Google Scholar 

  25. 25.

    Cantoni, C. et al. Electron transfer and ionic displacements at the origin of the 2D electron gas at the LAO/STO interface: Direct measurements with atomic-column spatial resolution. Adv. Mater. 24, 3952–3957 (2012).

    Article  Google Scholar 

  26. 26.

    Cancellieri, C. et al. Electrostriction at the LaAlO3/SrTiO3 interface. Phys. Rev. Lett. 107, 056102 (2011).

    Article  Google Scholar 

  27. 27.

    Yu, L. & Zunger, A. A polarity induced defect mechanism for conductivity and magnetism at polar–nonpolar oxide interfaces. Nat. Commun. 5, 5118 (2015).

    Article  Google Scholar 

  28. 28.

    Hernandez, T. et al. Localization of two-dimensional electron gas in LaAlO3/SrTiO3 heterostructures. Phys. Rev. B 85, 161407(R) (2012).

    Article  Google Scholar 

  29. 29.

    Popovic, Z. S. et al. Origin of the two-dimensional electron gas carrier density at the LaAlO3 on SrTiO3 interface. Phys. Rev. Lett. 101, 256801 (2008).

    Article  Google Scholar 

Download references

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

Authors

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.

Additional information

Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Supplementary information

Supplementary Information

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

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Song, K., Ryu, S., Lee, H. et al. Direct imaging of the electron liquid at oxide interfaces. Nature Nanotech 13, 198–203 (2018). https://doi.org/10.1038/s41565-017-0040-8

Download citation

Further reading

Search

Quick links

Find nanotechnology articles, nanomaterial data and patents all in one place. Visit Nano by Nature Research