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Tailoring the nature and strength of electron–phonon interactions in the SrTiO3(001) 2D electron liquid

Nature Materials volume 15, pages 835–839 (2016)Cite this article

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Abstract

Surfaces and interfaces offer new possibilities for tailoring the many-body interactions that dominate the electrical and thermal properties of transition metal oxides1,2,3,4. Here, we use the prototypical two-dimensional electron liquid (2DEL) at the SrTiO3(001) surface5,6,7 to reveal a remarkably complex evolution of electron–phonon coupling with the tunable carrier density of this system. At low density, where superconductivity is found in the analogous 2DEL at the LaAlO3/SrTiO3 interface8,9,10,11,12,13, our angle-resolved photoemission data show replica bands separated by 100 meV from the main bands. This is a hallmark of a coherent polaronic liquid and implies long-range coupling to a single longitudinal optical phonon branch. In the overdoped regime the preferential coupling to this branch decreases and the 2DEL undergoes a crossover to a more conventional metallic state with weaker short-range electron–phonon interaction. These results place constraints on the theoretical description of superconductivity and allow a unified understanding of the transport properties in SrTiO3-based 2DELs.

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Figure 1: A two-dimensional liquid of large polarons in SrTiO3.
Figure 2: Evolution of the 2DEL spectral function with carrier concentration.
Figure 3: Effective mass and quasiparticle residue in the SrTiO3 2DEL.

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Acknowledgements

We thank A. Fête, M. Grilli, L. Patthey, V. Strocov, J.-M. Triscone, D. van der Marel and Z. Zhong for discussions. The ARPES work was supported by the Swiss National Science Foundation (200021-146995). The spectral function calculations were supported at SLAC and Stanford University by the US Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, under Contract No. DE-AC02-76SF00515, and by the Computational Materials and Chemical Sciences Network (CMCSN), under Contract No. DE-SC0007091. A portion of the computational work was performed using the resources of the National Energy Research Scientific Computing Center supported by the US Department of Energy, Office of Science, under Contract No. DE-AC02-05CH11231. M.S. acknowledges financial support by the Sino-Swiss Science and Technology Cooperation (No. IZLCZ2138954), J.S.-B. by the Impuls- und Vernetzungsfonds der Helmholtz Gemeinschaft (Grant No. HRJRG-408), P.D.C.K. by the UK-EPSRC (EP/I031014/1) and the Royal Society, U.D. by the ERC Advanced Grant ‘OxideSurfaces’ and W.M. by the Thailand Research Fund (TRF) under the TRF Senior Research Scholar, Grant No. RTA5680008. We acknowledge Diamond Light Source for time on beamline I05 under proposal SI11741.

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Authors and Affiliations

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

    Z. Wang, N. C. Plumb, M. Shi, J. Mesot, M. Radovic & F. Baumberger

  2. Department of Quantum Matter Physics, University of Geneva, 24 Quai Ernest-Ansermet, 1211 Geneva 4, Switzerland

    Z. Wang, S. McKeown Walker, A. Tamai, F. Y. Bruno, A. de la Torre, S. Riccò & F. Baumberger

  3. Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA

    Y. Wang, B. Moritz & T. P. Devereaux

  4. Department of Applied Physics, Stanford University, Stanford, California 94305, USA

    Y. Wang

  5. Institute of Condensed Matter Physics, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland

    Z. Ristic & J. Mesot

  6. Helmholtz-Zentrum Berlin für Materialien und Energie, Elektronenspeicherring BESSY-II, 12489 Berlin, Germany

    P. Hlawenka, J. Sánchez-Barriga & A. Varykhalov

  7. Diamond Light Source, Harwell Campus, Didcot OX11 0DE, UK

    T. K. Kim & M. Hoesch

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

    P. D. C. King & F. Baumberger

  9. School of Physics and NANOTEC-SUT Center of Excellence on Advanced Functional Nanomaterials, Suranaree University of Technology, Nakhon Ratchasima 30000, Thailand

    W. Meevasana

  10. Institute of Applied Physics, Vienna University of Technology, Wiedner Hauptstrasse 8-10/134, A-1040 Vienna, Austria

    U. Diebold

  11. Laboratory for Solid State Physics, ETH Zürich, CH-8093 Zürich, Switzerland

    J. Mesot

  12. Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California 94305, USA

    T. P. Devereaux

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

    M. Radovic

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Contributions

ARPES measurements were carried out by Z.W., S.M.W., Z.R., F.Y.B., A.d.l.T., S.R., M.R. and F.B. and analysed by Z.W., A.T. and F.B.; N.C.P., M.S., P.H., J.S.-B., A.V., T.K.K. and M.H. were responsible for the synchrotron beam lines used in the experiments; Y.W., B.M. and T.P.D. performed the exact diagonalization calculations. F.B. wrote the manuscript with contributions by Z.W., Y.W. and A.T.; T.P.D., M.R. and F.B. were responsible for project planning, direction and resources. All authors contributed to the scientific discussion of the results.

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Correspondence to Z. Wang or F. Baumberger.

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Wang, Z., McKeown Walker, S., Tamai, A. et al. Tailoring the nature and strength of electron–phonon interactions in the SrTiO3(001) 2D electron liquid. Nature Mater 15, 835–839 (2016). https://doi.org/10.1038/nmat4623

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