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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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.
The authors declare no competing financial interests.
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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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