Letter | Published:

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

Abstract

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.

Access optionsAccess options

Rent or Buy article

Get time limited or full article access on ReadCube.

from$8.99

All prices are NET prices.

References

  1. 1.

    et al. Interface induced high temperature superconductivity in single unit-cell FeSe films on SrTiO3. Chin. Phys. Lett. 29, 037402 (2012)

  2. 2.

    et al. Electronic origin of high-temperature superconductivity in single-layer FeSe superconductor. Nature Commun. 3, 931 (2012)

  3. 3.

    et al. Phase diagram and electronic indication of high-temperature superconductivity at 65K in single-layer FeSe films. Nature Mater. 12, 605–610 (2013)

  4. 4.

    et al. Interface-induced superconductivity and strain-dependent spin density waves in FeSe/SrTiO3 thin films. Nature Mater. 12, 634–640 (2013)

  5. 5.

    , , & Large phonon band gap in SrTiO3 and the vibrational signatures of ferroelectricity in ATiO3 perovskites: first-principles lattice dynamics and inelastic neutron scattering. Phys. Rev. B 77, 134111 (2008)

  6. 6.

    , , & Ab initio linear response study of SrTiO3. Ferroelectrics 194, 109–118 (1997)

  7. 7.

    Neutron inelastic scattering study of the lattice dynamics of strontium titanate: harmonic models. J. Phys. C 5, 2711–2730 (1972)

  8. 8.

    & symmetry and the pairing mechanism. Phys. Rev. B 54, 14971–14973 (1996)

  9. 9.

    et al. Specific heat of Ca0.32Na0.68Fe2As2 single crystals: unconventional s± multiband superconductivity with intermediate repulsive interband coupling and sizable attractive intraband couplings. Phys. Rev. B 89, 134507 (2014)

  10. 10.

    , & Effect of an electron-phonon interaction on the one-electron spectral weight of a d-wave superconductor. Phys. Rev. B 69, 094523 (2004)

  11. 11.

    et al. Systematic study of electron-phonon coupling to oxygen modes across the cuprates. Phys. Rev. B 82, 064513 (2010)

  12. 12.

    , , & Density-of-states-driven anisotropies induced by momentum decoupling in Bi2Sr2CaCu2O8. Phys. Rev. B 54, R6877–R6880 (1996)

  13. 13.

    , , & Small-q phonon-mediated unconventional superconductivity in the iron pnictides. Phys. Rev. B 83, 092505 (2011)

  14. 14.

    , , & s- and d-wave symmetries of the solutions of the Eliashberg equations. Physica C 259, 253–264 (1996)

  15. 15.

    et al. Superconductivity in the PbO-type structure α-FeSe. Proc. Natl Acad. Sci. USA 105, 14262–14264 (2008)

  16. 16.

    , , & Phenomenology of the low-energy spectral function in high-Tc superconductors. Phys. Rev. B 57, R11093–R11096 (1998)

  17. 17.

    , & Occupied and unoccupied band structure of Ag(100) determined by photoemission from Ag quantum wells and bulk samples. Phys. Rev. B 61, 1804–1810 (2000)

  18. 18.

    , , , & Umklapp-mediated quantization of electronic state in Ag films on Ge(111). Phys. Rev. Lett. 96, 216803 (2006)

  19. 19.

    Molecular Photoelectron Spectroscopy (Wiley, 1970)

  20. 20.

    , , , & Structure and correlation effects in semiconducting SrTiO3. Phys. Rev. B 81, 235109 (2010)

  21. 21.

    et al. Unusual band renormalization in the simplest iron based superconductor. Preprint at (2013)

  22. 22.

    , , , & High-temperature superconductivity at the FeSe/SrTiO3 interface. Phys. Rev. B 86, 134508 (2012)

  23. 23.

    & Concepts relating magnetic interactions, intertwined electronic orders, and strongly correlated superconductivity. Proc. Natl Acad. Sci. USA 110, 17623–17630 (2013)

  24. 24.

    , & Fermiology, orbital order, orbital fluctuations, and cooper pairing in iron-based superconductors. Phys. Rev. B 88, 100504 (2013)

  25. 25.

    , , , & Superconductivity at the border of electron localization and itinerancy. Nature Commun. 4, 2783 (2013)

  26. 26.

    et al. Doping dependence of spin excitations and its correlations with high-temperature superconductivity in iron pnictides. Nature Commun. 4, 2874 (2013)

  27. 27.

    et al. Nodeless superconducting gap in AxFe2Se2 (A = K,Cs) revealed by angle-resolved photoemission spectroscopy. Nature Mater. 10, 273–277 (2011)

Download references

Acknowledgements

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.

Affiliations

  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

Authors

  1. Search for J. J. Lee in:

  2. Search for F. T. Schmitt in:

  3. Search for R. G. Moore in:

  4. Search for S. Johnston in:

  5. Search for Y.-T. Cui in:

  6. Search for W. Li in:

  7. Search for M. Yi in:

  8. Search for Z. K. Liu in:

  9. Search for M. Hashimoto in:

  10. Search for Y. Zhang in:

  11. Search for D. H. Lu in:

  12. Search for T. P. Devereaux in:

  13. Search for D.-H. Lee in:

  14. Search for Z.-X. Shen in:

Contributions

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

Supplementary information

PDF files

  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.

About this article

Publication history

Received

Accepted

Published

DOI

https://doi.org/10.1038/nature13894

Further reading

Comments

By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.