At the interface between complex insulating oxides, novel phases with interesting properties may occur, such as the metallic state reported in the LaAlO3/SrTiO3 system 1. Although this state has been predicted 2 and reported3,4 to be confined at the interface, some studies indicate a much broader spatial extension5, thereby questioning its origin. Here, we provide for the first time a direct determination of the carrier density profile of this system through resistance profile mappings collected in cross-section LaAlO3/SrTiO3 samples with a conducting-tip atomic force microscope (CT-AFM). We find that, depending on specific growth protocols, the spatial extension of the high-mobility electron gas can be varied from hundreds of micrometres into SrTiO3 to a few nanometres next to the LaAlO3/SrTiO3 interface. Our results emphasize the potential of CT-AFM as a novel tool to characterize complex oxide interfaces and provide us with a definitive and conclusive way to reconcile the body of experimental data in this system.
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G.H. acknowledges financial support from the DURSI (Generalitat de Catalunya, Spain). Financial support from PAI- France-Croatia COGITO Program No. 82/240083, Croatian MZOS Project No. 119-1191458-1023 and the French Agence Nationale de la Recherche (Project Pnano ALICANTE) is acknowledged. We thank Y. Gourdel for his help in the polishing process. The authors acknowledge J. N. Eckstein for valuable comments.
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Basletic, M., Maurice, JL., Carrétéro, C. et al. Mapping the spatial distribution of charge carriers in LaAlO3/SrTiO3 heterostructures. Nature Mater 7, 621–625 (2008). https://doi.org/10.1038/nmat2223
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