Letter | Published:

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

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


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.

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

Author information


  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


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Correspondence to C. L. Chien.

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