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Extreme mobility enhancement of two-dimensional electron gases at oxide interfaces by charge-transfer-induced modulation doping

Abstract

Two-dimensional electron gases (2DEGs) formed at the interface of insulating complex oxides promise the development of all-oxide electronic devices. These 2DEGs involve many-body interactions that give rise to a variety of physical phenomena such as superconductivity, magnetism, tunable metal–insulator transitions and phase separation. Increasing the mobility of the 2DEG, however, remains a major challenge. Here, we show that the electron mobility is enhanced by more than two orders of magnitude by inserting a single-unit-cell insulating layer of polar La1−xSrxMnO3 (x = 0, 1/8, and 1/3) at the interface between disordered LaAlO3 and crystalline SrTiO3 produced at room temperature. Resonant X-ray spectroscopy and transmission electron microscopy show that the manganite layer undergoes unambiguous electronic reconstruction, leading to modulation doping of such atomically engineered complex oxide heterointerfaces. At low temperatures, the modulation-doped 2DEG exhibits Shubnikov–de Haas oscillations and fingerprints of the quantum Hall effect, demonstrating unprecedented high mobility and low electron density.

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Figure 1: Atomically engineered complex oxide interfaces with a single-unit-cell manganite buffer layer.
Figure 2: Electronic properties of d-LAO (8.5 nm)/STO heterostructures with and without LSMO (x = 0, 1/8, and 1/3) buffer layers.
Figure 3: Electronic reconstructions in d-LAO/STO heterostructures.
Figure 4: Modulation doping of STO-based heterostructures.
Figure 5: Quantum oscillations at modulation-doped oxide interfaces.

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Acknowledgements

The authors gratefully acknowledge discussions with J. Mannhart, J. R. Sun and B. G. Shen, and technical assistance from J. Geyti, L. Han, K. V. Hansen, S. Upadhyay, C. Olsen and A. Jellinggaard. This work was funded by the European Union (EU) Council under the 7th Framework Program (FP7) grant number NMP3-LA-2010-246102 IFOX, by funding from the European Research Council (ERC) under FP7, ERC grant No. 246791—COUNTATOMS and ERC Starting Grant 278510 VORTEX. The Qu-Ant-EM microscope was partly funded by the Hercules Fund from the Flemish Government. The authors acknowledge also financial support from EU under FP7 under a contract for an Integrated Infrastructure Initiative. Reference No. 312483-ESTEEM2. Funding from the Fund for Scientific Research Flanders is acknowledged for FWO project G.0044.13N (‘Charge ordering’). Funding from the Danish Agency for Science, Technology and Innovation, and the Lundbeck Foundation are acknowledged. The Center for Quantum Devices is supported by the Danish National Research Foundation. The Canadian work was supported by NSERC and the Max Planck-UBC Centre for Quantum Materials. Some experiments for this work were performed at the Canadian Light Source, which is funded by the Canada Foundation for Innovation, NSERC, the National Research Council of Canada, the Canadian Institutes of Health Research, the Government of Saskatchewan, Western Economic Diversification Canada, and the University of Saskatchewan.

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Contributions

Y.Z.C.: concept design, film growth, transport measurements, data analysis, interpretation and writing of the manuscript. The contributions of other authors are as follows. Transport measurements and analysis: D.V.C., N.H.A., M.Huijben, J.A.S., M.Honig and S.I.; STEM and EELS measurements and analysis: N.G., R.E., J.V. and G.V.T.; XPS measurements and analysis: T.W., G.K., M.Huijben, G.R. and N.B.; RXR measurements and analysis: R.J.G., S.M., F.H., R.S. and G.A.S.; SdH measurements: F.T., G.E.D.K.P. and T.S.J.; Data discussion: N.P. and S.L. All authors extensively discussed the results and the manuscript.

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Correspondence to Y. Z. Chen.

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Chen, Y., Trier, F., Wijnands, T. et al. Extreme mobility enhancement of two-dimensional electron gases at oxide interfaces by charge-transfer-induced modulation doping. Nature Mater 14, 801–806 (2015). https://doi.org/10.1038/nmat4303

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