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Mapping spin–charge conversion to the band structure in a topological oxide two-dimensional electron gas

Abstract

While spintronics has traditionally relied on ferromagnetic metals as spin generators and detectors, spin–orbitronics exploits the efficient spin–charge interconversion enabled by spin–orbit coupling in non-magnetic systems. Although the Rashba picture of split parabolic bands is often used to interpret such experiments, it fails to explain the largest conversion effects and their relationship with the electronic structure. Here, we demonstrate a very large spin-to-charge conversion effect in an interface-engineered, high-carrier-density SrTiO3 two-dimensional electron gas and map its gate dependence on the band structure. We show that the conversion process is amplified by enhanced Rashba-like splitting due to orbital mixing and in the vicinity of avoided band crossings with topologically non-trivial order. Our results indicate that oxide two-dimensional electron gases are strong candidates for spin-based information readout in new memory and transistor designs. Our results also emphasize the promise of topology as a new ingredient to expand the scope of complex oxides for spintronics.

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Fig. 1: Characterization of AlOx/STO 2D electron gases.
Fig. 2: Magnetotransport properties.
Fig. 3: Spin–charge conversion in NiFe/AlOx/STO.
Fig. 4: Electronic and spin structure of the 2DEG.
Fig. 5: Energy dependence of the spin–charge conversion.

Data availability

The data that support the findings of this study are available from the corresponding author on reasonable request.

Code availability

The self-written code that generated the data for Figs. 4f,g and 5b,c is available from A.J. upon reasonable request.

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Acknowledgements

This work received support from the ERC Consolidator Grant no. 615759 ‘MINT’, the QUANTERA project ‘QUANTOX’, the French ANR programme through projects OISO (ANR-17-CE24-0026-03), TOPRISE (ANR-16-CE24-0017) and the Laboratoire d’Excellence LANEF (ANR-10-LABX-51-01). M.B. thanks the Alexander von Humboldt Foundation for supporting his stays at Martin-Luther-Universität Halle. F.T. acknowledges support by research grant no. VKR023371 (SPINOX) from VILLUM FONDEN. A.J., B.G. and I.M. acknowledge support by Priority Program SPP 1666 and SFB 762 of Deutsche Forschungsgemeinschaft. D.C.V. thanks the French Ministry of Higher Education and Research and CNRS for financing his PhD thesis. We thank H. Jaffrès for insightful comments on tunnel escape times, M. Sing for his help with XPS analysis and E. Schierle for his assistance with X-ray absorption spectroscopy measurements.

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M.B. proposed and supervised the study with help from L.V., J.-P.A., A.B. and A.F. D.C.V. prepared the samples with the help of F.T. and L.M.V.-A. and performed XPS experiments and analysed the data with A.S. D.C.V., G.S. and N.B. measured the magnetotransport properties and analysed the results. H.O. prepared the samples for STEM and EELS and performed the observations and spectroscopy measurements. S.V. performed the X-ray absorption measurements and analysed the data. S.M.-W., F.Y.B. and F.B. performed the ARPES measurements and their analysis. P.N. performed the spin-pumping experiments and analysed the data with D.C.V., L.V., J.-P.A. and M.B. P.B., M.V. and M.G. conducted the Poisson–Schrödinger calculations. A.J. and B.G. performed the tight-binding and Boltzmann calculations under the supervision of I.M., with input from M.V., M.G. and M.B. D.C.V. and M.B. wrote the manuscript with input from all authors. All authors discussed the results and contributed to their interpretation.

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Correspondence to Laurent Vila or Manuel Bibes.

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Supplementary Figs. 1–15, Notes 1–12 and refs. 1–13

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Vaz, D.C., Noël, P., Johansson, A. et al. Mapping spin–charge conversion to the band structure in a topological oxide two-dimensional electron gas. Nat. Mater. 18, 1187–1193 (2019). https://doi.org/10.1038/s41563-019-0467-4

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