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Giant spin splitting of the two-dimensional electron gas at the surface of SrTiO3

Nature Materials volume 13, pages 1085–1090 (2014)Cite this article

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Abstract

Two-dimensional electron gases (2DEGs) forming at the interfaces of transition metal oxides1,2,3 exhibit a range of properties, including tunable insulator–superconductor–metal transitions4,5,6, large magnetoresistance7, coexisting ferromagnetism and superconductivity8,9, and a spin splitting of a few meV (refs 10, 11). Strontium titanate (SrTiO3), the cornerstone of such oxide-based electronics, is a transparent, non-magnetic, wide-bandgap insulator in the bulk, and has recently been found to host a surface 2DEG (refs 12, 13, 14, 15). The most strongly confined carriers within this 2DEG comprise two subbands, separated by an energy gap of 90 meV and forming concentric circular Fermi surfaces12,13,15. Using spin- and angle-resolved photoemission spectroscopy (SARPES), we show that the electron spins in these subbands have opposite chiralities. Although the Rashba effect might be expected to give rise to such spin textures, the giant splitting of almost 100 meV at the Fermi level is far larger than anticipated16,17. Moreover, in contrast to a simple Rashba system, the spin-polarized subbands are non-degenerate at the Brillouin zone centre. This degeneracy can be lifted by time-reversal symmetry breaking, implying the possible existence of magnetic order. These results show that confined electronic states at oxide surfaces can be endowed with novel, non-trivial properties that are both theoretically challenging to anticipate and promising for technological applications.

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Figure 1: Spin-polarized subbands of the 2DEG at the surface of SrTiO3.
Figure 2: Spin components at different subband binding energies.
Figure 3: Summary of spin splittings and spin vectors of the light subbands at the surface of SrTiO3.

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Acknowledgements

We thank M. Gabay, M. Rozenberg, N. Reyren, R. Claessen, S. Ming, L. Patthey and J. Mesot for discussions. Experiments were conducted at the Surface/Interface Spectroscopy (SIS) beamline of the Swiss Light Source within the Paul Scherrer Institut in Villigen, Switzerland. The COPHEE end-station is supported by the Swiss National Science Foundation. Work at the CSNSM is supported by public grants from the French National Research Agency (ANR) (project LACUNES No ANR-13-BS04-0006-01) and the ‘Laboratoire d’Excellence Physique Atomes Lumière Matière’ (LabEx PALM project ELECTROX) overseen by the ANR as part of the ‘Investissements d’Avenir’ program (reference: ANR-10-LABX-0039). T.C.R. is supported by the RTRA–Triangle de la Physique (project PEGASOS). J.H.D. acknowledges support from the Swiss National Science Foundation. A.F.S-S. acknowledges support from the Institut Universitaire de France.

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Authors and Affiliations

  1. CSNSM, Université Paris-Sud and CNRS/IN2P3, Bâtiments 104 et 108, 91405 Orsay cedex, France

    A. F. Santander-Syro, F. Fortuna, C. Bareille & T. C. Rödel

  2. Synchrotron SOLEIL, L’Orme des Merisiers, Saint-Aubin-BP48, 91192 Gif-sur-Yvette, France

    T. C. Rödel

  3. Physik-Institut, Universität Zürich, Winterthurerstrasse 190 8057 Zürich, Switzerland,

    G. Landolt & J. H. Dil

  4. Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland

    G. Landolt, N. C. Plumb, J. H. Dil & M. Radović

  5. Institute of Condensed Matter Physics, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland

    J. H. Dil & M. Radović

  6. SwissFEL, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland

    M. Radović

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  1. A. F. Santander-Syro
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Contributions

Project conception: A.F.S-S., F.F., J.H.D. and M.R.; measurements: A.F.S-S., F.F., C.B., T.C.R., G.L., N.C.P., J.H.D. and M.R.; infrastructure for SARPES experiments at SLS: G.L. and J.H.D.; sample characterizations: N.C.P. and M.R.; data analysis: A.F.S-S., F.F. and J.H.D.; writing of the manuscript: A.F.S-S., F.F. and J.H.D. All authors extensively discussed the results and the manuscript.

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Correspondence to A. F. Santander-Syro, J. H. Dil or M. Radović.

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Santander-Syro, A., Fortuna, F., Bareille, C. et al. Giant spin splitting of the two-dimensional electron gas at the surface of SrTiO3. Nature Mater 13, 1085–1090 (2014). https://doi.org/10.1038/nmat4107

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