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Interfacial mode coupling as the origin of the enhancement of Tc in FeSe films on SrTiO3

Nature volume 515, pages 245248 (13 November 2014) | Download Citation


Films of iron selenide (FeSe) one unit cell thick grown on strontium titanate (SrTiO3 or STO) substrates have recently shown1,2,3,4 superconducting energy gaps opening at temperatures close to the boiling point of liquid nitrogen (77 kelvin), which is a record for the iron-based superconductors. The gap opening temperature usually sets the superconducting transition temperature Tc, as the gap signals the formation of Cooper pairs, the bound electron states responsible for superconductivity. To understand why Cooper pairs form at such high temperatures, we examine the role of the SrTiO3 substrate. Here we report high-resolution angle-resolved photoemission spectroscopy results that reveal an unexpected characteristic of the single-unit-cell FeSe/SrTiO3 system: shake-off bands suggesting the presence of bosonic modes, most probably oxygen optical phonons in SrTiO3 (refs 5, 6, 7), which couple to the FeSe electrons with only a small momentum transfer. Such interfacial coupling assists superconductivity in most channels, including those mediated by spin fluctuations8,9,10,11,12,13,14. Our calculations suggest that this coupling is responsible for raising the superconducting gap opening temperature in single-unit-cell FeSe/SrTiO3.

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This work was supported by the US Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division. D.-H.L. is supported by the Department of Energy, Office of Basic Energy Sciences, Division of Materials Science, under the Quantum Material programme DE-AC02-05CH11231. Measurements were performed at the Stanford Synchrotron Radiation Lightsource, a national user facility operated by Stanford University on behalf of the US Department of Energy, Office of Basic Energy Sciences.

Author information

Author notes

    • J. J. Lee
    • , F. T. Schmitt
    •  & R. G. Moore

    These authors contributed equally to this work.


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

    • J. J. Lee
    • , F. T. Schmitt
    • , R. G. Moore
    • , Y.-T. Cui
    • , W. Li
    • , M. Yi
    • , Z. K. Liu
    • , Y. Zhang
    • , T. P. Devereaux
    •  & Z.-X. Shen
  2. Departments of Physics and Applied Physics, and Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California 94305, USA

    • J. J. Lee
    • , M. Yi
    • , Z. K. Liu
    •  & Z.-X. Shen
  3. Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada

    • S. Johnston
  4. Quantum Matter Institute, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada

    • S. Johnston
  5. Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996-1200, USA

    • S. Johnston
  6. Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA

    • M. Hashimoto
    •  & D. H. Lu
  7. Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA

    • Y. Zhang
  8. Department of Physics, University of California at Berkeley, Berkeley, California 94720, USA

    • D.-H. Lee
  9. Material Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA

    • D.-H. Lee


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J.J.L., F.T.S. and R.G.M. grew films, collected and analysed data, and wrote the paper. S.J. and D.-H.L. performed theory calculations. Y.T.C, W.L., Z.K.L., Y.Z., D.H.L. and M.Y. provided discussion about data and interpretation. M.H. and D.H.L. provided experimental support at Stanford Synchrotron Radiation Lightsource. All authors participated in the discussion of results. Project direction was provided by D.-H.L., T.P.D. and Z.-X.S.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Z.-X. Shen.

Extended data

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  1. 1.

    Supplementary Information

    This file contains Supplementary Text and Data 1-8 and additional references. It includes growth and measurement methods, discussion about additional angle-resolved photoemission spectroscopy data taken on films, and detailed theoretical treatment about electron-phonon coupling and its enhancement of the superconducting transition temperature. The supplementary information references the extended data figures, whose legends are attached in the main manuscript text.

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