Letter | Published:

Identifying the 'fingerprint' of antiferromagnetic spin fluctuations in iron pnictide superconductors

Nature Physics volume 11, pages 177182 (2015) | Download Citation



Cooper pairing in the iron-based high-Tc superconductors1,2,3 is often conjectured to involve bosonic fluctuations. Among the candidates are antiferromagnetic spin fluctuations1,4,5 and d-orbital fluctuations amplified by phonons6,7. Any such electron–boson interaction should alter the electron’s ‘self-energy’, and then become detectable through consequent modifications in the energy dependence of the electron’s momentum and lifetime8,9,10. Here we introduce a novel theoretical/experimental approach aimed at uniquely identifying the relevant fluctuations of iron-based superconductors by measuring effects of their self-energy. We use innovative quasiparticle interference (QPI) imaging11 techniques in LiFeAs to reveal strongly momentum-space anisotropic self-energy signatures that are focused along the Fe–Fe (interband scattering) direction, where the spin fluctuations of LiFeAs are concentrated. These effects coincide in energy with perturbations to the density of states N(ω) usually associated with the Cooper pairing interaction. We show that all the measured phenomena comprise the predicted QPI ‘fingerprint’ of a self-energy due to antiferromagnetic spin fluctuations, thereby distinguishing them as the predominant electron–boson interaction.

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We are especially grateful to A. P. Mackenzie and D. J. Scalapino for key guidance with this project. We acknowledge and thank D. H. Lee, A. Chubukov, P. J. Hirschfeld, M. Norman and J. Schmalian for helpful discussions and communications. Theoretical studies are supported by the US Department of Energy, Office of Basic Energy Sciences, Division of Materials Science and Engineering under Award DE-SC0010313 (K.L. and E-A.K.); NSF DMR-1120296 to the Cornell Center for Materials Research and NSF CAREER grant DMR-0955822 (M.H.F.). Experimental studies are supported by the Center for Emergent Superconductivity, an Energy Frontier Research Center, headquartered at Brookhaven National Laboratory and funded by the US Department of Energy, under DE-2009-BNL-PM015; by the UK EPSRC; by a Grant-in-Aid for Scientific Research C (No. 22540380) from the Japan Society for the Promotion of Science. T-M.C. acknowledges support by NSC101-2112-M-001-029-MY3.

Author information

Author notes

    • M. P. Allan
    • , Kyungmin Lee
    •  & A. W. Rost

    These authors contributed equally to this work.


  1. LASSP, Department of Physics, Cornell University, Ithaca, New York 14853, USA

    • M. P. Allan
    • , Kyungmin Lee
    • , A. W. Rost
    • , M. H. Fischer
    • , F. Massee
    • , J. C. Davis
    •  & Eun-Ah Kim
  2. CMPMS Department, Brookhaven National Laboratory, Upton, New York 11973, USA

    • M. P. Allan
    • , F. Massee
    •  & J. C. Davis
  3. School of Physics and Astronomy, University of St Andrews, St Andrews, Fife KY16 9SS, Scotland

    • A. W. Rost
    •  & J. C. Davis
  4. Department of Physics, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan

    • A. W. Rost
  5. Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki 305-8568, Japan

    • K. Kihou
    • , C-H. Lee
    • , A. Iyo
    •  & H. Eisaki
  6. JST, Transformative Research-Project on Iron Pnictides (TRIP), Tokyo 102-0075, Japan

    • K. Kihou
    • , C-H. Lee
    • , A. Iyo
    •  & H. Eisaki
  7. Institute of Physics, Academia Sinica, Nankang, Taipei 11529, Taiwan

    • T-M. Chuang
  8. Kavli Institute at Cornell for Nanoscale Science, Cornell University, Ithaca, New York 14853, USA

    • J. C. Davis


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M.P.A., A.W.R., F.M. and T-M.C. performed the experiments and analysed the data; K.K., A.I., C-H.L. and H.E. synthesized the samples; K.L. and M.H.F. performed the theoretical calculations of the self-energy and simulation of quasiparticle interference. This project was initiated by the experimental discovery of the strongly anisotropic QPI features in the electron–boson energy range (A.W.R.) and by the resulting hypothesis that they are self-energy effects; J.C.D. and E-A.K. supervised the investigation and wrote the paper with contributions from M.P.A., A.W.R., F.M., K.L. and M.H.F. The manuscript reflects the contributions of all authors.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Eun-Ah Kim.

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