Tunable spin polarization and superconductivity in engineered oxide interfaces

Abstract

Advances in growth technology of oxide materials allow single atomic layer control of heterostructures. In particular delta doping, a key materials’ engineering tool in today’s semiconductor technology, is now also available for oxides. Here we show that a fully electric-field-tunable spin-polarized and superconducting quasi-2D electron system (q2DES) can be artificially created by inserting a few unit cells of delta doping EuTiO3 at the interface between LaAlO3 and SrTiO3 oxides1,2. Spin polarization emerges below the ferromagnetic transition temperature of the EuTiO3 layer (TFM = 6–8 K) and is due to the exchange interaction between the magnetic moments of Eu-4f and of Ti-3d electrons. Moreover, in a large region of the phase diagram, superconductivity sets in from a ferromagnetic normal state. The occurrence of magnetic interactions, superconductivity and spin–orbit coupling in the same q2DES makes the LaAlO3/EuTiO3/SrTiO3 system an intriguing platform for the emergence of novel quantum phases in low-dimensional materials.

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Figure 1: STEM–EELS analysis and X-ray linear dichroism of LAO/ETO/STO heterostructures.
Figure 2: X-ray magnetic circular dichroism of LAO/ETO/STO heterostructures.
Figure 3: Square resistance and 2D-conductance versus gate voltage.
Figure 4: Hall-effect data as a function of the gate voltage and temperature.
Figure 5: Superconductivity and phase diagram.

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Acknowledgements

We received funding from the Ministero dell’Istruzione, dell’Università e della Ricerca for the FIRB 2012 project HybridNanoDev (Grant No. RBFR1236VV), FIRB 2011 project ‘Oxides at the nanoscale: multifunctionality and applications’ (Grant No. RBAP115AYN) and for the PRIN 2010-11 project (Grant No. PRIN 2010-11–OXIDE). The X-ray absorption measurements were performed on the EPFL/PSI X-Treme beamline at the Swiss Light Source, Paul Scherrer Institut, Villigen, Switzerland. The research of C.C. was supported by the US Department of Energy, Basic Energy Sciences, Materials Sciences and Engineering Division. The research of B.J. was supported by CNRS under PICS-0754.

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The samples were prepared by E.D.G., G.M.D.L. and F.M.G., and were characterized by R.D.C., I.P. and D.S. C.C. performed the STEM and EELS experiments and interpreted the data. G.M.D.L., D.Marrè, C.P., S.R. and M.S. carried out the X-ray spectroscopy experiments. M.S., S.R. and G.G. analysed the X-ray spectroscopy data. D.S. was responsible for transport measurements under field effect and data analysis, with D.Massarotti and F.T. for dilution temperatures measurements, and with B.J. for the magneto-transport characterizations and analysis. All the authors contributed to the interpretation of the data. M.S. and D.S. wrote the manuscript. The project was coordinated by M.S.

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Correspondence to D. Stornaiuolo or M. Salluzzo.

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The authors declare no competing financial interests.

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Stornaiuolo, D., Cantoni, C., De Luca, G. et al. Tunable spin polarization and superconductivity in engineered oxide interfaces. Nature Mater 15, 278–283 (2016). https://doi.org/10.1038/nmat4491

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