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Hybridization-controlled charge transfer and induced magnetism at correlated oxide interfaces

Abstract

At interfaces between conventional materials, band bending and alignment are classically controlled by differences in electrochemical potential. Applying this concept to oxides in which interfaces can be polar and cations may adopt a mixed valence has led to the discovery of novel two-dimensional states between simple band insulators such as LaAlO3 and SrTiO3. However, many oxides have a more complex electronic structure, with charge, orbital and/or spin orders arising from strong Coulomb interactions at and between transition metal and oxygen ions. Such electronic correlations offer a rich playground to engineer functional interfaces but their compatibility with the classical band alignment picture remains an open question. Here we show that beyond differences in electron affinities and polar effects, a key parameter determining charge transfer at correlated oxide interfaces is the energy required to alter the covalence of the metal–oxygen bond. Using the perovskite nickelate (RNiO3) family as a template, we probe charge reconstruction at interfaces with gadolinium titanate GdTiO3. X-ray absorption spectroscopy shows that the charge transfer is thwarted by hybridization effects tuned by the rare-earth (R) size. Charge transfer results in an induced ferromagnetic-like state in the nickelate, exemplifying the potential of correlated interfaces to design novel phases. Further, our work clarifies strategies to engineer two-dimensional systems through the control of both doping and covalence.

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Figure 1: Growth and structural characterization.
Figure 2: Interfacial charge transfer in LaNiO3/GdTiO3.
Figure 3: Tuning interfacial charge transfer by the rare earth in the nickelate.
Figure 4: Covalence versus ionicity.
Figure 5: Induced magnetic moment in the nickelates.
Figure 6: Role of covalence on magnetism.

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Acknowledgements

The authors thank M. Watanabe for the Digital Micrograph PCA plug-in, F. Y. Bruno for his assistance at an early stage of this project and V. Garcia and R. Mattana for useful comments. The research leading to these results has received funding from the European Community’s Seventh Framework Programme (FP7/2007-2013) under grant agreement #312284. Research at CNRS/Thales was supported by the ERC Consolidator Grant #615759 ‘MINT’ and the region Île-de-France DIM ‘Oxymore’ (project NEIMO). Research at ORNL was supported by the US Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division. Work at UCM was supported by grants MAT2014-52405-C02-01 and Consolider Ingenio 2010—CSD2009-00013 (Imagine), by CAM through grant CAM S2013/MIT-2740 and by the ERC Starting Investigator Grant #239739 STEMOX. J.S. thanks the Institute of Physics of CNRS for supporting his stay at CNRS/Thales. We acknowledge synchrotron SOLEIL (proposal no. 20140194) and HZB for provision of synchrotron radiation facilities and the Labex PALM.

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M.B. and M.N.G. designed and conceived the experiment. M.N.G. carried out sample growth and characterization. G.S.-S. and M.V. carried out STEM and EELS analysis. M.N.G., S.V., E.W., E.S., R.A., A.A., A.B., M.B. and J.S. carried out XAS, XRMS and XMCD measurements and data analysis. M.N.G., J.E.R., J.-P.R., J.S. and M.B. carried out photoemission measurements and data analysis. J.V. performed first-principles calculations. M.B., M.N.G. and J.S. wrote the article with inputs from all authors.

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Correspondence to M. Bibes.

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Grisolia, M., Varignon, J., Sanchez-Santolino, G. et al. Hybridization-controlled charge transfer and induced magnetism at correlated oxide interfaces. Nature Phys 12, 484–492 (2016). https://doi.org/10.1038/nphys3627

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