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Observation of a ubiquitous three-dimensional superconducting gap function in optimally doped Ba0.6K0.4Fe2As2

Nature Physics volume 7, pages 198–202 (2011)Cite this article

Abstract

The iron-pnictide superconductors have a layered structureformed by stacks of FeAs planes from which the superconductivity originates. Given the multiband and quasi three-dimensional1 (3D) electronic structure of these high-temperature superconductors, knowledge of the quasi-3D superconducting (SC) gap is essential for understanding the superconducting mechanism. By using the kz capability of angle-resolved photoemission, we completely determined the SC gap on all five Fermi surfaces (FSs) in three dimensions on Ba0.6K0.4Fe2As2 samples. We found a marked kz dispersion of the SC gap, which can derive only from interlayer pairing. Remarkably, the SC energy gaps can be described by a single 3D gap function with two energy scales characterizing the strengths of intralayer Δ1 and interlayer Δ2 pairing. The anisotropy ratio Δ1/Δ2, determined from the gap function, is close to the c-axis anisotropy ratio of the magnetic exchange coupling Jc/Ja b in the parent compound2. The ubiquitous gap function for all the 3D FSs reveals that pairing is short-ranged and strongly constrains the possible pairing force in the pnictides. A suitable candidate could arise from short-range antiferromagnetic fluctuations.

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Figure 1: Band dispersion of superconducting Ba0.6K0.4Fe2As2.
Figure 2: kz dispersion of quasiparticles and Fermi surface warping.
Figure 3: kz dependence of the superconducting gaps.
Figure 4: 3D superconducting gap function Δ (kx, ky, kz).

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Acknowledgements

We thank X. Dai, B. A. Bernevig and Z. Fang for valuable discussions. This work was supported by grants from the Chinese Academy of Sciences, NSF, the Ministry of Science and Technology of China, NSF, DOE of US, and the Sino-Swiss Science and Technology Cooperation.

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Authors and Affiliations

  1. Department of Physics, Boston College, Chestnut Hill, Massachusetts 02467, USA

    Y-M. Xu & Z. Wang

  2. Beijing National Laboratory for Condensed Matter Physics, and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China

    Y-B. Huang, P. Zheng, N-L. Wang, P-C. Dai, J-P. Hu & H. Ding

  3. Swiss Light Source, Paul Scherrer Institute, CH-5232 Villigen, Switzerland

    Y-B. Huang, X-Y. Cui, E. Razzoli, M. Radovic & M. Shi

  4. Laboratory for Synchrotron and Neutron Spectroscopy, EPF Lausanne, CH-1015 Lausanne, Switzerland

    E. Razzoli & M. Radovic

  5. Department of Physics, Renmin University of China, Beijing 100872, China

    G-F. Chen

  6. Department of Physics and Astronomy, The University of Tennessee, Knoxville, Tennessee 37996, USA

    C-L. Zhang & P-C. Dai

  7. Neutron Scattering Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA

    P-C. Dai

  8. Department of Physics, Purdue University, West Lafayette, Indiana 47907, USA

    J-P. Hu

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Contributions

Y-M.X., Y-B.H., X-Y.C., E.R. and M.R. carried out the experiments. Y-M.X. and Y-B.H. analysed the data. H.D., Y-M.X., J-P.H. and Z.W. designed the experiments. Z.W., H.D., Y-M.X. and J-P.H. wrote the paper. G-F.C., P.Z., N-L.W., C-L.Z. and P-C.D. synthesized materials. All authors discussed the results and commented on the manuscript.

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Correspondence to H. Ding.

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Xu, YM., Huang, YB., Cui, XY. et al. Observation of a ubiquitous three-dimensional superconducting gap function in optimally doped Ba0.6K0.4Fe2As2. Nature Phys 7, 198–202 (2011). https://doi.org/10.1038/nphys1879

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