Letter | Published:

A BCS-like gap in the superconductor SmFeAsO0.85F0.15

Nature volume 453, pages 12241227 (26 June 2008) | Download Citation

Abstract

Since the discovery of superconductivity in the high-transition-temperature (high-Tc) copper oxides two decades ago, it has been firmly established that the CuO2 plane is essential for superconductivity and gives rise to a host of other very unusual properties. A new family of superconductors with the general composition of LaFeAsO1-xFx has recently been discovered1,2,3,4,5,6,7,8 and the conspicuous lack of the CuO2 planes raises the tantalizing question of a different pairing mechanism in these oxypnictides. The superconducting gap (its magnitude, structure, and temperature dependence) is intimately related to pairing. Here we report the observation of a single gap in the superconductor SmFeAsO0.85F0.15 with Tc = 42 K as measured by Andreev spectroscopy. The gap value of 2Δ = 13.34 ± 0.3 meV gives 2Δ/kBTc = 3.68 (where kB is the Boltzmann constant), close to the Bardeen–Cooper–Schrieffer (BCS) prediction of 3.53. The gap decreases with temperature and vanishes at Tc in a manner consistent with the BCS prediction, but dramatically different from that of the pseudogap behaviour in the copper oxide superconductors. Our results clearly indicate a nodeless gap order parameter, which is nearly isotropic in size across different sections of the Fermi surface, and are not compatible with models involving antiferromagnetic fluctuations, strong correlations, the t-J model, and the like, originally designed for the high-Tc copper oxides.

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.

    , , & Iron-based layered superconductor La[O1-xFx]FeAsx (x = 0.05–0.12) with Tc = 26 K. J. Am. Chem. Soc. 130, 3296–3297 (2008)

  2. 2.

    , , , & Superconductivity at 25 K in hole doped La1-xSrxOFeAs. Preprint at 〈〉 (2008)

  3. 3.

    et al. Superconductivity at 43 K in samarium-arsenide oxides SmFeAsO1-xFx. Preprint at 〈〉 (2008)

  4. 4.

    et al. Superconductivity at 41 K and its competition with spin-density-wave instability in layered CeO1-xFxFeAs. Preprint at 〈〉 (2008)

  5. 5.

    et al. Superconductivity at 52 K in iron-based F-doped layered quaternary compound Pr[O1-xFx]FeAs. Preprint at 〈〉 (2008)

  6. 6.

    et al. Superconductivity at 55 K in iron-based F-doped layered quaternary compound Sm[O1-xFx]FeAs. Preprint at 〈〉 (2008)

  7. 7.

    et al. Phase diagram and quantum critical point in newly discovered superconductors: SmO1-xFxFeAs. Preprint at 〈〉 (2008)

  8. 8.

    et al. Novel superconductivity and phase diagram in the iron-based arsenic-oxides ReFeAsO1-delta (Re = rare earth metal) without F-doping. Preprint at 〈〉 (2008)

  9. 9.

    et al. Magnetic order versus superconductivity in the iron-based layered La(O1-xFx)FeAs systems. Preprint at 〈〉 (2008)

  10. 10.

    , , & Unconventional sign-reversing superconductivity in LaFeAsO1-xFx. Preprint at 〈〉 (2008)

  11. 11.

    et al. Evidence for two superconducting energy gaps in MgB2 by point-contact spectroscopy. Phys. Rev. Lett. 87, 137005 (2001)

  12. 12.

    , , , & Andreev reflections at metal/superconductor point contacts: Measurement and analysis. Phys. Rev. B 63, 104510 (2001)

  13. 13.

    , & Transition from metallic to tunneling regimes in superconducting microconstrictions: Excess current, charge imbalance, and supercurrent conversion. Phys. Rev. B 25, 4515–4532 (1982)

  14. 14.

    , , , & Finite-quasiparticle-lifetime effects in the differential conductance of Bi2Sr2CaCu2Oy/Au junctions. Phys. Rev. B 49, 10016–10019 (1994)

  15. 15.

    The size effect and the non-local Boltzmann transport equation in orifice and disk geometry. Proc. Phys. Soc. 89, 927–941 (1966)

  16. 16.

    Andreev-Saint-James reflections: A probe of cuprate superconductors. Rev. Mod. Phys. 77, 109–135 (2005)

  17. 17.

    et al. Tunneling spectroscopy in AlNiCo decagonal quasicrystals. Phys. Rev. Lett. 82, 1229–1232 (1999)

  18. 18.

    , & Subgap and above-gap differential resistance anomalies in superconductor-normal-metal microjunctions. Phys. Rev. Lett. 71, 1907–1910 (1993)

  19. 19.

    et al. Unconventional pairing symmetry in iron-based layered superconductor LaO0.9F0.1-deltaFeAs revealed by point-contact spectroscopy measurements. Preprint at 〈〉 (2008)

  20. 20.

    , , & in Coherence in High Temperature Superconductors (eds Deutscher, G. & Revcolevschi, A.) 428–442 (World Scientific, Singapore, 1996)

  21. 21.

    , , & Scanning tunneling spectroscopy of high-temperature superconductors. Rev. Mod. Phys. 79, 353–419 (2007)

Download references

Acknowledgements

This work was supported by the US National Science Foundation and the Natural Science Foundation of China.

Author information

Affiliations

  1. Department of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland 21218, USA

    • T. Y. Chen
    • , Z. Tesanovic
    •  & C. L. Chien
  2. Hefei National Laboratory for Physical Sciences at Microscale and Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026, China

    • R. H. Liu
    •  & X. H. Chen

Authors

  1. Search for T. Y. Chen in:

  2. Search for Z. Tesanovic in:

  3. Search for R. H. Liu in:

  4. Search for X. H. Chen in:

  5. Search for C. L. Chien in:

Corresponding author

Correspondence to C. L. Chien.

Supplementary information

PDF files

  1. 1.

    Supplementary Information

    This file contains Supplementary Data and Supplementary Figures 1-3 with Legends.

About this article

Publication history

Received

Accepted

Published

DOI

https://doi.org/10.1038/nature07081

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.