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Built-in and induced polarization across LaAlO3/SrTiO3 heterojunctions

Nature Physics volume 7, pages 80–86 (2011)Cite this article

Abstract

Ionic crystals terminated at oppositely charged polar surfaces are inherently unstable and expected to undergo surface reconstructions to maintain electrostatic stability. Essentially, an electric field that arises between oppositely charged atomic planes gives rise to a built-in potential that diverges with thickness. Here we present evidence of such a built-in potential across polar LaAlO3 thin films grown on SrTiO3 substrates, a system well known for the electron gas that forms at the interface. By carrying out tunnelling measurements between the electron gas and metallic electrodes on LaAlO3 we measure a built-in electric field across LaAlO3 of 80.1 meV Å−1. In addition, capacitance measurements reveal the presence of an induced dipole moment across the heterostructure. We foresee use of the ionic built-in potential as an additional tuning parameter in both existing and future device architectures, especially as atomic control of oxide interfaces gains widespread momentum.

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Figure 1: Built-in polarization across LaAlO3/SrTiO3 tunnel junction diodes.
Figure 2: Thickness-dependent built-in potential and interband tunnelling across polar LaAlO3.
Figure 3: Tuning the tunnelling current across LaAlO3 by tuning the SrTiO3 permittivity and charge density.
Figure 4: Capacitance measurements agree with J V and also reveal an induced dipole across the heterostructure.

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Acknowledgements

We thank J. H. Bardarson, M. Gajek and R. Dynes at UC Berkeley as well as X. Du at Stonybrook for discussions and comments on the manuscript. G.S-B. acknowledges support from the Japan Society for Promotion of Science (Award No. SP08057) and the US National Science Foundation (Award No. OISE0812816) as part of the 2008 E.A.P.S.I. fellowship program, under which this work was commenced. W.S. acknowledges support from the Dutch Organization for Scientific Research (NWO-Rubicon Grant). The work at Berkeley (R.R.) was supported by the US Department of Energy under contract No. DE-AC02-05CH1123. The work at Florida (A.F.H.) was supported by the US National Science Foundation under Grant No. 0404962.

Author information

Authors and Affiliations

  1. Department of Physics, University of California, Berkeley, California 94720, USA

    Guneeta Singh-Bhalla, Wolter Siemons & Ramamoorthy Ramesh

  2. Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA

    Guneeta Singh-Bhalla, Jayakanth Ravichandran & Ramamoorthy Ramesh

  3. Department of Advanced Materials Science, University of Tokyo, Kashiwa, Chiba 277-8561, Japan

    Guneeta Singh-Bhalla, Christopher Bell, Yasuyuki Hikita & Harold Y. Hwang

  4. Department of Physics, University of Florida, Gainesville, Florida 32611, USA

    Guneeta Singh-Bhalla & Arthur F. Hebard

  5. Japan Science and Technology Agency, Kawaguchi, 332-0012, Japan

    Christopher Bell & Harold Y. Hwang

  6. Applied Science and Technology Graduate Group, University of California, Berkeley, California 94720, USA

    Jayakanth Ravichandran

  7. Department of Electrical Engineering and Computer Sciences, University of California, Berkeley, California 94720, USA

    Sayeef Salahuddin

  8. Department of Materials Science and Engineering, University of California, Berkeley, California 94720, USA

    Ramamoorthy Ramesh

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Contributions

C.B. deposited the LaAlO3 films. G.S-B. prepared and measured the tunnel junctions with C.B., modelled the data with J.R. and analysed the J V curves with J.R. and W.S. S.S. simulated the J V curves within the non-equilibrium Green’s function approach. The manuscript was prepared by G.S-B. with assistance/input from C.B., J.R., W.S. and Y.H. H.Y.H., A.F.H. and G.S-B. contributed to conceptualizing the experiment. H.Y.H. provided insights and expertise on the LaAlO3/SrTiO3 interface, R.R. on ferroelectricity and A.F.H. on interpreting complex impedance.

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Correspondence to Guneeta Singh-Bhalla.

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Singh-Bhalla, G., Bell, C., Ravichandran, J. et al. Built-in and induced polarization across LaAlO3/SrTiO3 heterojunctions. Nature Phys 7, 80–86 (2011). https://doi.org/10.1038/nphys1814

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