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Critical spin fluctuations and the origin of nematic order in Ba(Fe1−xCox)2As2

Nature Physics volume 12, pages 560–563 (2016)Cite this article

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Abstract

Nematic fluctuations and order play a prominent role in material classes such as the cuprates1, some ruthenates2 or the iron-based compounds3,4,5,6 and may be interrelated with superconductivity7,8,9,10,11. In iron-based compounds12 signatures of nematicity have been observed in a variety of experiments. However, the fundamental question as to the relevance of the related spin13, charge9,14 or orbital8,15,16 fluctuations remains open. Here, we use inelastic light (Raman) scattering and study Ba(Fe1−xCox)2As2 (0 ≤ x ≤ 0.085) for getting direct access to nematicity and the underlying critical fluctuations with finite characteristic wavelengths17,18,19,20,21. We show that the response from fluctuations appears only in B1g (x2 − y2) symmetry (1 Fe unit cell). The scattering amplitude increases towards the structural transition at Ts but vanishes only below the magnetic ordering transition at TSDW < Ts, suggesting a magnetic origin of the fluctuations. The theoretical analysis explains the selection rules and the temperature dependence of the fluctuation response. These results make magnetism the favourite candidate for driving the series of transitions.

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Figure 1: Raman results of Ba(Fe0.975Co0.025)2As2.
Figure 2: Fluctuation contribution to the Raman response of Ba(Fe0.975Co0.025)2As2.
Figure 3: Higher-order Aslamazov–Larkin diagrams for interacting fluctuations.
Figure 4: Temperature dependence of the initial slope of the fluctuation response.
Figure 5: Phase diagram of Ba(Fe1−xCox)2As2.

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Acknowledgements

We acknowledge useful discussions with T. P. Devereaux, Y. Gallais, S. A. Kivelson, B. Moritz and I. Paul. Financial support for the work came from the German Research Foundation DFG through the Priority Program SPP 1458 (project nos HA 2071/7 and SCHM 1035/5), from the Bavarian Californian Technology Center BaCaTeC (project no. A5 [2012-2]), and from the Transregional Collaborative Research Center TRR 80. U.K. and J.S. were supported by the Helmholtz Association, through the Helmholtz postdoctoral grant PD-075 ‘Unconventional order and superconductivity in pnictides’. R.H. thanks the Stanford Institute for Materials and Energy Sciences (SIMES) at Stanford University and SLAC National Accelerator Laboratory for hospitality. Work in the SIMES at Stanford University and SLAC was supported by the US Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, under Contract No. DE-AC02-76SF00515.

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Author notes

  1. B. Muschler & J. G. Analytis

    Present address: Present addresses: Zoller & Fröhlich GmbH, Simoniusstrasse 22, 88239 Wangen im Allgäu, Germany (B.M.); Department of Physics, University of California, Berkeley, California 94720, USA (J.G.A.).,

Authors and Affiliations

  1. Walther Meissner Institut, Bayerische Akademie der Wissenschaften, 85748 Garching, Germany

    F. Kretzschmar, T. Böhm, B. Muschler, A. Baum, D. Jost & R. Hackl

  2. Fakultät für Physik E23, Technische Universität München, 85748 Garching, Germany

    F. Kretzschmar, T. Böhm, B. Muschler, A. Baum & D. Jost

  3. Institute for Theoretical Condensed Matter Physics (TKM) and Institut für Festkörperphysik, Karlsruhe Institute of Technology (KIT), 76128 Karlsruhe, Germany

    U. Karahasanović & J. Schmalian

  4. Department of Physics, University of Rome “Sapienza”, 00185 Roma, Italy

    S. Caprara, M. Grilli & C. Di Castro

  5. Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA

    J. G. Analytis, J.-H. Chu & I. R. Fisher

  6. Geballe Laboratory for Advanced Materials & Department of Applied Physics, Stanford University, California 94305, USA

    J. G. Analytis, J.-H. Chu & I. R. Fisher

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  1. F. Kretzschmar
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Contributions

F.K., T.B., B.M., A.B. and D.J. contributed approximately equally to the experiments. U.K., J.S., S.C., M.G. and C.D.C. developed the theory. J.-H.C., J.G.A. and I.R.F. prepared and characterized the samples. F.K., T.B. and R.H. conceived the study. U.K., F.K., T.B. and R.H. prepared the manuscript.

Corresponding author

Correspondence to R. Hackl.

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The authors declare no competing financial interests.

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Kretzschmar, F., Böhm, T., Karahasanović, U. et al. Critical spin fluctuations and the origin of nematic order in Ba(Fe1−xCox)2As2. Nature Phys 12, 560–563 (2016). https://doi.org/10.1038/nphys3634

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