Letter | Published:

Maximal Rashba-like spin splitting via kinetic-energy-coupled inversion-symmetry breaking

Nature volume 549, pages 492496 (28 September 2017) | Download Citation

Abstract

Engineering and enhancing the breaking of inversion symmetry in solids—that is, allowing electrons to differentiate between ‘up’ and ‘down’—is a key goal in condensed-matter physics and materials science because it can be used to stabilize states that are of fundamental interest and also have potential practical applications. Examples include improved ferroelectrics for memory devices and materials that host Majorana zero modes for quantum computing1,2. Although inversion symmetry is naturally broken in several crystalline environments, such as at surfaces and interfaces, maximizing the influence of this effect on the electronic states of interest remains a challenge. Here we present a mechanism for realizing a much larger coupling of inversion-symmetry breaking to itinerant surface electrons than is typically achieved. The key element is a pronounced asymmetry of surface hopping energies—that is, a kinetic-energy-coupled inversion-symmetry breaking, the energy scale of which is a substantial fraction of the bandwidth. Using spin- and angle-resolved photoemission spectroscopy, we demonstrate that such a strong inversion-symmetry breaking, when combined with spin–orbit interactions, can mediate Rashba-like3,4 spin splittings that are much larger than would typically be expected. The energy scale of the inversion-symmetry breaking that we achieve is so large that the spin splitting in the CoO2- and RhO2-derived surface states of delafossite oxides becomes controlled by the full atomic spin–orbit coupling of the 3d and 4d transition metals, resulting in some of the largest known Rashba-like3,4 spin splittings. The core structural building blocks that facilitate the bandwidth-scaled inversion-symmetry breaking are common to numerous materials. Our findings therefore provide opportunities for creating spin-textured states and suggest routes to interfacial control of inversion-symmetry breaking in designer heterostructures of oxides and other material classes.

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Acknowledgements

We thank N. Nandi and B. Schmidt for discussions. We acknowledge support from the European Research Council (through the QUESTDO project), the Engineering and Physical Sciences Research Council, UK (grant no. EP/I031014/1), the Royal Society, the Max-Planck Society and the International Max-Planck Partnership for Measurement and Observation at the Quantum Limit. V.S., L.B., O.J.C. and J.M.R. acknowledge EPSRC for PhD studentship support through grant numbers EP/L015110/1, EP/G03673X/1, EP/K503162/1 and EP/L505079/1. D.K. acknowledges funding by the DFG within FOR 1346. We thank Diamond Light Source and Elettra synchrotrons for access to Beamlines I05 (proposal numbers SI12469, SI14927 and SI18267) and APE (proposal no. 20150019), respectively, that contributed to the results presented here. Additional supporting measurements were performed at the CASIOPEE beamline of SOLEIL, and we are grateful to I. Marković and P. Le Fèvre for their assistance.

Author information

Affiliations

  1. SUPA, School of Physics and Astronomy, University of St Andrews, St Andrews KY16 9SS, UK

    • Veronika Sunko
    • , F. Mazzola
    • , L. Bawden
    • , O. J. Clark
    • , J. M. Riley
    • , A. P. Mackenzie
    •  & P. D. C. King
  2. Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Straße 40, 01187 Dresden, Germany

    • Veronika Sunko
    • , H. Rosner
    • , P. Kushwaha
    • , S. Khim
    • , D. Kasinathan
    • , M. W. Haverkort
    •  & A. P. Mackenzie
  3. Diamond Light Source, Harwell Campus, Didcot OX11 0DE, UK

    • J. M. Riley
    • , T. K. Kim
    •  & M. Hoesch
  4. Institute for Theoretical Physics, Heidelberg University, Philosophenweg 19, 69120 Heidelberg, Germany

    • M. W. Haverkort
  5. Istituto Officina dei Materiali (IOM)-CNR, Laboratorio TASC, Area Science Park, S.S.14, Km 163.5, 34149 Trieste, Italy

    • J. Fujii
    •  & I. Vobornik

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Contributions

V.S., F.M., L.B., O.J.C., J.M.R. and P.D.C.K. measured the experimental data, and V.S. performed the data analysis. P.K and S.K. grew and characterized the samples. V.S. developed the tight-binding models, and H.R., D.K. and M.W.H. performed the first-principles calculations. M.H. and T.K.K. maintained the ARPES end station and J.F. and I.V. the spin-ARPES end station, and all provided experimental support. V.S., P.D.C.K. and A.P.M. wrote the manuscript with input and discussion from co-authors, and were responsible for overall project planning and direction.

Competing interests

The authors declare no competing financial interests.

Corresponding authors

Correspondence to A. P. Mackenzie or P. D. C. King.

Reviewer Information Nature thanks A. MacDonald and the other anonymous reviewer(s) for their contribution to the peer review of this work.

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DOI

https://doi.org/10.1038/nature23898

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