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Orbital-driven nematicity in FeSe

Nature Materials volume 14, pages 210–214 (2015)Cite this article

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Abstract

A fundamental and unconventional characteristic of superconductivity in iron-based materials is that it occurs in the vicinity of two other instabilities. In addition to a tendency towards magnetic order, these Fe-based systems have a propensity for nematic ordering: a lowering of the rotational symmetry while time-reversal invariance is preserved. Setting the stage for superconductivity, it is heavily debated whether the nematic symmetry breaking is driven by lattice, orbital or spin degrees of freedom. Here, we report a very clear splitting of NMR resonance lines in FeSe at Tnem = 91 K, far above the superconducting Tc of 9.3 K. The splitting occurs for magnetic fields perpendicular to the Fe planes and has the temperature dependence of a Landau-type order parameter. Spin–lattice relaxation rates are not affected at Tnem, which unequivocally establishes orbital degrees of freedom as driving the nematic order. We demonstrate that superconductivity competes with the emerging nematicity.

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Figure 1: Schematic crystallographic structure of FeSe.
Figure 2: 77Se NMR spectra for the FeSe single crystal.
Figure 3: Emergence of orbital-driven nematic state in FeSe.
Figure 4: Top view of the FOO in FeSe with the two different domains that are present in a twinned crystal.

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Acknowledgements

The authors thank G. Prando and H-J. Grafe for discussion. This work has been supported by the Deutsche Forschungsgemeinschaft (Germany) through DFG Research Grants BA 4927/1-1 and the Priority Program SPP 1458. Financial support through the DFG Research Training Group GRK 1621 is gratefully acknowledged. The work at POSTECH was supported by the National Research Foundation (NRF) through the Mid-Career Researcher Program (No. 2012-013838), SRC Center for Topological Matter (No. 2011-0030046), and the Max Planck POSTECH/KOREA Research Initiative Program (No. 2011-0031558), and also by the Institute of Basic Science (IBS) through the Center for Artificial Low Dimensional Electronic Systems.

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Authors and Affiliations

  1. IFW Dresden, Helmholtzstr. 20, 01069 Dresden, Germany

    S-H. Baek, D. V. Efremov, Jeroen van den Brink & B. Büchner

  2. Department of Physics, Pohang University of Science and Technology, Pohang 790-784, Korea

    J. M. Ok & J. S. Kim

  3. Department of Physics, Technische Universität Dresden, 01062 Dresden, Germany

    Jeroen van den Brink & B. Büchner

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  1. S-H. Baek
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  2. D. V. Efremov
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Contributions

S-H.B. performed the main NMR measurements, analysed data, and participated in writing of the manuscript; J.M.O. and J.S.K. synthesized the sample; D.V.E. and J.v.d.B. provided theoretical support and participated in writing of the manuscript; B.B. supervised and guided the study and participated in the writing of the manuscript. All authors discussed the results and commented on the manuscript.

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Correspondence to S-H. Baek.

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Baek, SH., Efremov, D., Ok, J. et al. Orbital-driven nematicity in FeSe. Nature Mater 14, 210–214 (2015). https://doi.org/10.1038/nmat4138

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