Anisotropic spin fluctuations in detwinned FeSe


Superconductivity in FeSe emerges from a nematic phase that breaks four-fold rotational symmetry in the iron plane. This phase may arise from orbital ordering, spin fluctuations or hidden magnetic quadrupolar order. Here we use inelastic neutron scattering on a mosaic of single crystals of FeSe, detwinned by mounting on a BaFe2As2 substrate to demonstrate that spin excitations are most intense at the antiferromagnetic wave vectors QAF = (±1, 0) at low energies E = 6–11 meV in the normal state. This two-fold (C2) anisotropy is reduced at lower energies, 3–5 meV, indicating a gapped four-fold (C4) mode. In the superconducting state, however, the strong nematic anisotropy is again reflected in the spin resonance (E = 3.6 meV) at QAF with incommensurate scattering around 5–6 meV. Our results highlight the extreme electronic anisotropy of the nematic phase of FeSe and are consistent with a highly anisotropic superconducting gap driven by spin fluctuations.

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Fig. 1: Crystal structure, Fermi surface and neutron scattering of FeSe.
Fig. 2: Low-energy spin fluctuations in twinned FeSe below and above Tc.
Fig. 3: Normal-state spin fluctuations in detwinned FeSe.
Fig. 4: Effect of superconductivity on low-energy spin fluctuations of detwinned FeSe.
Fig. 5: Theoretical calculations of the spin fluctuations in detwinned FeSe.

Data availability

The data that support the plots in this paper and other findings of this study are available from the corresponding authors on reasonable request.


  1. 1.

    Scalapino, D. J. A common thread: the pairing interaction for unconventional superconductors. Rev. Mod. Phys. 84, 1383 (2012).

    CAS  Article  Google Scholar 

  2. 2.

    Dai, P. C. Antiferromagnetic order and spin dynamics in iron-based superconductors. Rev. Mod. Phys. 87, 855 (2015).

    CAS  Article  Google Scholar 

  3. 3.

    Chu, J.-H. et al. In-plane resistivity anisotropy in an underdoped iron arsenide superconductor. Science 329, 824–826 (2010).

    CAS  Article  Google Scholar 

  4. 4.

    Kuo, H.-H., Chu, J.-H., Palmstrom, J. C., Kivelson, S. A. & Fisher, I. R. Ubiquitous signatures of nematic quantum criticality in optimally doped Fe-based superconductors. Science 352, 958–962 (2016).

    CAS  Article  Google Scholar 

  5. 5.

    Fernandes, R. M., Chubukov, A. V. & Schmalian, J. What drives nematic order in iron-based superconductors? Nat. Phys. 10, 97–104 (2014).

    CAS  Article  Google Scholar 

  6. 6.

    Böhmer, A. E. & Meingast, C. Electronic nematic susceptibility of iron-based superconductors. C. R. Phys. 17, 90–112 (2016).

    Article  Google Scholar 

  7. 7.

    Hsu, F. C. et al. Superconductivity in the PbO-type structure α-FeSe. Proc. Natl Acad. Sci. USA 105, 14262 (2008).

    CAS  Article  Google Scholar 

  8. 8.

    McQueen, T. M. et al. Tetragonal-to-orthorhombic structural phase transition at 90 K in the superconductor Fe1.01Se. Phys. Rev. Lett. 103, 057002 (2009).

    CAS  Article  Google Scholar 

  9. 9.

    Böhmer, A. E. & Kreisel, A. Nematicity, magnetism and superconductivity in FeSe. J. Phys.: Condens. Matter 30, 023001 (2018).

    Google Scholar 

  10. 10.

    Lee, C. C., Yin, W.-G. & Ku, W. Ferro-orbital order and strong magnetic anisotropy in the parent compounds of iron-pnictide superconductors. Phys. Rev. Lett. 103, 267001 (2009).

    Article  Google Scholar 

  11. 11.

    Baek, S.-H. et al. Orbital-driven nematicity in FeSe. Nat. Mater. 14, 210–214 (2015).

    CAS  Article  Google Scholar 

  12. 12.

    Böhmer, A. E. et al. Origin of the tetragonal-to-orthorhombic phase transition in FeSe: a combined thermodynamic and NMR study of nematicity. Phys. Rev. Lett. 114, 027001 (2015).

    Article  Google Scholar 

  13. 13.

    Yamakawa, Y., Onari, S. & Kontani, H. Nematicity and magnetism in FeSe and other families of Fe-based superconductors. Phys. Rev. X 6, 021032 (2016).

    Google Scholar 

  14. 14.

    Onari, S., Yamakawa, Y. & Kontani, H. Sign-reversing orbital polarization in the nematic phase of FeSe due to the C 2 symmetry breaking in the self-energy. Phys. Rev. Lett. 116, 227001 (2016).

    Article  Google Scholar 

  15. 15.

    Kontani, H. & Onari, S. Orbital-fluctuation-mediated superconductivity in iron pnictides: analysis of the five-orbital Hubbard-Holstein model. Phys. Rev. Lett. 104, 157001 (2010).

    Article  Google Scholar 

  16. 16.

    Wang, F., Kivelson, S. & Lee, D.-H. Nematicity and quantum paramagnetism in FeSe. Nat. Phys. 11, 959–963 (2015).

    CAS  Article  Google Scholar 

  17. 17.

    Glasbrenner, J. K. et al. Effect of magnetic frustration on nematicity and superconductivity in iron chalcogenides. Nat. Phys. 11, 953–958 (2015).

    CAS  Article  Google Scholar 

  18. 18.

    Wang, Q. et al. Magnetic ground state of FeSe. Nat. Commun. 7, 12182 (2016).

    CAS  Article  Google Scholar 

  19. 19.

    She, J.-H., Lawler, M. J. & Kim, E.-A. Quantum spin liquid intertwining nematic and superconducting order in FeSe. Phys. Rev. Lett. 121, 237002 (2018).

    CAS  Article  Google Scholar 

  20. 20.

    Yi, M., Zhang, Y., Shen, Z.-X. & Lu, D. Role of the orbital degree of freedom in iron-based superconductors. npj Quantum Mater. 2, 57 (2017).

    Article  Google Scholar 

  21. 21.

    Coldea, A. & Watson, M. D. The key ingredients of the electronic structure of FeSe. Annu. Rev. Condens. Matter Phys. 9, 125–146 (2018).

    CAS  Article  Google Scholar 

  22. 22.

    Liu, D. F. et al. Orbital origin of extremely anisotropic superconducting gap in nematic phase of FeSe superconductor. Phys. Rev. X 8, 031033 (2018).

    CAS  Google Scholar 

  23. 23.

    Song, C. L. et al. Imaging the electron boson coupling in superconducting FeSe films using a scanning tunneling microscope. Phys. Rev. Lett. 112, 057002 (2014).

    Article  Google Scholar 

  24. 24.

    Sprau, P. O. et al. Discovery of orbital-selective Cooper pairing in FeSe. Science 357, 75–80 (2017).

    CAS  Article  Google Scholar 

  25. 25.

    Kostin, A. et al. Visualizing orbital-selective quasiparticle interference in the Hund’s metal state of FeSe. Nat. Mater. 17, 869–874 (2018).

    CAS  Article  Google Scholar 

  26. 26.

    Wang, Z. T., Hu, W. J. & Nevidomskyy, A. H. Spin ferroquadrupolar order in the nematic phase of FeSe. Phys. Rev. Lett. 116, 247203 (2016).

    Article  Google Scholar 

  27. 27.

    Lai, H.-H., Hu, W. J., Nica, E. M., Yu, R. & Si, Q. Antiferroquadrupolar order and rotational symmetry breaking in a generalized bilinear-biquadratic model on a square lattice. Phys. Rev. Lett. 118, 176401 (2017).

    Article  Google Scholar 

  28. 28.

    Kreisel, A., Mukherjee, S., Hirschfeld, P. J. & Andersen, B. M. Spin excitations in a model of FeSe with orbital ordering. Phys. Rev. B 92, 224515 (2015).

    Article  Google Scholar 

  29. 29.

    Mukherjee, S., Kreisel, A., Hirschfeld, P. J. & Andersen, B. M. Model of electronic structure and superconductivity in orbitally ordered FeSe. Phys. Rev. Lett. 115, 026402 (2015).

    Article  Google Scholar 

  30. 30.

    Hirschfeld, P. J. Using gap symmetry and structure to reveal the pairing mechanism in Fe-based superconductors. C. R. Phys. 17, 197–231 (2016).

    CAS  Article  Google Scholar 

  31. 31.

    Kreisel, A., Andersen, B. M. & Hirschfeld, P. J. Itinerant approach to magnetic neutron scattering of FeSe: effect of orbital selectivity. Phys. Rev. B 98, 214518 (2018).

    CAS  Article  Google Scholar 

  32. 32.

    Wang, Q. et al. Strong interplay between stripe spin fluctuations, nematicity and superconductivity in FeSe. Nat. Mater. 15, 159–163 (2016).

    CAS  Article  Google Scholar 

  33. 33.

    Ma, M. W. et al. Prominent role of spin-orbit coupling in FeSe revealed by inelastic neutron scattering. Phys. Rev. X 7, 021025 (2017).

    Google Scholar 

  34. 34.

    Zhang, R. et al. Neutron spin resonance as a probe of Fermi surface nesting and superconducting gap symmetry in Ba0.67K0.33(Fe1−xCox)2As2. Phys. Rev. B 98, 060502(R) (2018).

    Article  Google Scholar 

  35. 35.

    Nica, E. M., Yu, R. & Si, Q. Orbital-selective pairing and superconductivity in iron selenides. npj Quantum Mater. 2, 24 (2017).

    Article  Google Scholar 

  36. 36.

    Kreisel, A. et al. Orbital selective pairing and gap structures of iron-based superconductors. Phys. Rev. B 95, 174504 (2017).

    Article  Google Scholar 

  37. 37.

    Benfatto, L., Valenzuela, B. & Fanfarillo, L. Nematic pairing from orbital selective spin fluctuations in FeSe. npj Quantum Mater. 3, 56 (2018).

    Article  Google Scholar 

  38. 38.

    Kang, J., Fernandes, R. M. & Chubukov, A. Superconductivity in FeSe: the role of nematic order. Phys. Rev. Lett. 120, 267001 (2018).

    CAS  Article  Google Scholar 

  39. 39.

    Lu, X. Y. et al. Nematic spin correlations in the tetragonal state of uniaxial-strained BaFe2−xNixAs2. Science 345, 657 (2014).

    CAS  Article  Google Scholar 

  40. 40.

    Lu, X. Y. et al. Spin waves in detwinned BaFe2As2. Phys. Rev. Lett. 121, 067002 (2018).

    CAS  Article  Google Scholar 

  41. 41.

    Matan, K., Morinaga, R., Iida, K. & Sato, T. J. Anisotropic itinerant magnetism and spin fluctuations in BaFe2As2: a neutron scattering study. Phys. Rev. B 79, 054526 (2009).

    Article  Google Scholar 

  42. 42.

    Wang, C. et al. Longitudinal spin excitations and magnetic anisotropy in antiferromagnetically ordered BaFe2As2. Phys. Rev. X 3, 041036 (2013).

    Google Scholar 

  43. 43.

    Georges, A., de’ Medici, L. & Mravlje, J. Strong correlations from Hund’s coupling. Annu. Rev. Condens. Matter Phys. 4, 137–178 (2013).

    CAS  Article  Google Scholar 

  44. 44.

    de’ Medici, L. & Capone, M. in The Iron Pnictide Superconductors (eds Mancini, F. & Citro, R.) 186 (Springer, 2017).

  45. 45.

    van Roekeghem, A., Richard, P., Ding, H. & Biermann, S. Spectral properties of transition metal pnictides and chalcogenides: angle-resolved photoemission spectroscopy and dynamical mean-field theory. C. R. Phys. 17, 140 (2016).

    Article  Google Scholar 

  46. 46.

    Ishizuka, J., Yamada, T., Yanagi, Y. & Ono, Y. Fermi surface, pressure-induced antiferromagnetic order, and superconductivity in FeSe. J. Phys. Soc. Jpn 87, 014705 (2018).

    Article  Google Scholar 

  47. 47.

    Yu, R., Zhu, J.-X. & Si, Q. Orbital selectivity enhanced by nematic order in FeSe. Phys. Rev. Lett. 121, 227003 (2018).

    Article  Google Scholar 

  48. 48.

    Lake, B. et al. Spins in the vortices of a high-temperature superconductor. Science 291, 1759 (2001).

    CAS  Article  Google Scholar 

  49. 49.

    Kimura, H. et al. Novel in-gap spin state in Zn-doped La1.85Sr0.15CuO4. Phys. Rev. Lett. 91, 067002 (2003).

    CAS  Article  Google Scholar 

  50. 50.

    Andersen, B. M. et al. Disorder-induced freezing of dynamical spin fluctuations in cuprate materials. Phys. Rev. Lett. 105, 147002 (2010).

    Article  Google Scholar 

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We thank D. Abernathy, Q. Wang, Y. Hao and H. Hu for useful discussions. The neutron-scattering work at Rice University was supported by the US Department of Energy, BES DE-SC0012311 (P.D.). The single-crystal synthesis work was supported by Robert A. Welch Foundation grant no. C-1839 (P.D.). X.L. is supported by the National Natural Science Foundation of China under Grant No. 11734002. C.B. and Y.C. are supported by the US Department of Energy grant no. DE-FG02-08ER46544. B.M.A. acknowledges financial support from the Carlsberg Foundation. P.J.H. was supported by the Department of Energy under grant no. DE-FG02-05ER46236. This research used resources at the High Flux Isotope Reactor and Spallation Neutron Source, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. Access to MACS was provided by the Center for High Resolution Neutron Scattering, a partnership between the National Institute of Standards and Technology and the National Science Foundation under agreement No. DMR-1508249.

Author information




X.L., T.C. and P.D. conceived the project. T.C. prepared all the FeSe single-crystal samples. BaFe2As2 single crystals were prepared by T.C., X.L., R.Z., Y.L. and Y.R. Neutron-scattering experiments on twinned samples were carried out by T.C., Y.C., Y.Q., C.B. and P.D. at NCNR. Neutron-scattering experiments on detwinned samples were carried out by T.C., J.P., T.G.P., J.R.S., H.C., Y.W. and P.D. at Oak Ridge National Laboratory, ISIS and MLZ. Theoretical analysis was performed by A.K., B.M.A. and P.J.H. The entire project was supervised by P.D. The manuscript was written by P.D., T.C., A.K., B.M.A. and P.J.H. All authors made comments.

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Correspondence to Xingye Lu or Pengcheng Dai.

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Supplementary Notes 1 and 2, Supplementary Figs. 1–10 and Supplementary References 1–12.

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Chen, T., Chen, Y., Kreisel, A. et al. Anisotropic spin fluctuations in detwinned FeSe. Nat. Mater. 18, 709–716 (2019).

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