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Imaging orbital-selective quasiparticles in the Hund’s metal state of FeSe

Nature Materials volume 17, pages 869–874 (2018)Cite this article

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Abstract

Strong electronic correlations, emerging from the parent Mott insulator phase, are key to copper-based high-temperature superconductivity. By contrast, the parent phase of an iron-based high-temperature superconductor is never a correlated insulator. However, this distinction may be deceptive because Fe has five actived d orbitals while Cu has only one. In theory, such orbital multiplicity can generate a Hund’s metal state, in which alignment of the Fe spins suppresses inter-orbital fluctuations, producing orbitally selective strong correlations. The spectral weights Zm of quasiparticles associated with different Fe orbitals m should then be radically different. Here we use quasiparticle scattering interference resolved by orbital content to explore these predictions in FeSe. Signatures of strong, orbitally selective differences of quasiparticle Zm appear on all detectable bands over a wide energy range. Further, the quasiparticle interference amplitudes reveal that \(Z_{xy} < Z_{xz} \ll Z_{yz}\), consistent with earlier orbital-selective Cooper pairing studies. Thus, orbital-selective strong correlations dominate the parent state of iron-based high-temperature superconductivity in FeSe.

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Fig. 1: Orbitally resolved quasiparticle scattering interference (QPI) in FeSe.
Fig. 2: Visualizing orbital-selective quasiparticle interference (QPI).
Fig. 3: Energy dependence of orbital-selective quasiparticle interference (QPI).
Fig. 4: Detecting orbital-selective QPI from both ε- and δ-bands above Fermi energy Ef.
Fig. 5: Momentum-angle dependence of OSQP weight Zm.

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Acknowledgements

We are grateful to S.D. Edkins, A. Georges, M.H. Hamidian, J.E. Hoffman, G. Kotliar, E.-A. Kim, D.-H. Lee, L. de Medici, P. Phillips and J.-H. She for helpful discussions and communications. J.C.S.D. and P.C.C. acknowledge support from the Moore Foundation’s EPiQS (Emergent Phenomena in Quantum Physics) Initiative through Grant No. GBMF4544 and Grant No. GBMF4411, respectively. P.J.H. acknowledges support from DOE Grant No. DE-FG02-05ER46236. A.Kr. and B.M.A. acknowledge support from a Lundbeckfond Fellowship (Grant No. A9318). Material synthesis and detailed characterization at Ames National Laboratory was supported by the U.S. Department of Energy, Office of Basic Energy Science, Division of Materials Sciences and Engineering—Ames Laboratory is operated for the U.S. Department of Energy by Iowa State University under Contract No. DE-AC02-07CH11358; experimental studies carried out by the Center for Emergent Superconductivity, an Energy Frontier Research Center, headquartered at Brookhaven National Laboratory, were funded by the U.S. Department of Energy under Contract No. DE-2009-BNL-PM015.

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Author notes

  1. These authors contributed equally: A. Kostin, P.O. Sprau, A. Kreisel.

Authors and Affiliations

  1. Department of Physics, Cornell University, Ithaca, NY, USA

    A. Kostin, P. O. Sprau, Yi Xue Chong & J. C. Séamus Davis

  2. CMPMS Department, Brookhaven National Laboratory, Upton, NY, USA

    A. Kostin, P. O. Sprau, Yi Xue Chong & J. C. Séamus Davis

  3. Institut für Theoretische Physik, Universität Leipzig, Leipzig, Germany

    A. Kreisel

  4. Ames Laboratory, U.S. Department of Energy, Ames, IA, USA

    A. E. Böhmer & P. C. Canfield

  5. Karlsruhe Institute of Technology, Karlsruhe, Germany

    A. E. Böhmer

  6. Department of Physics and Astronomy, Iowa State University, Ames, IA, USA

    P. C. Canfield

  7. Department of Physics, University of Florida, Gainesville, FL, USA

    P. J. Hirschfeld

  8. Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark

    B. M. Andersen

  9. School of Physics and Astronomy, University of St. Andrews, Fife, UK

    J. C. Séamus Davis

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Contributions

A.Ko., Y.X.C. and P.O.S. developed and carried out the experiments; A.E.B. and P.C.C. synthesized and characterized the samples; A.Ko., P.O.S. and A.Kr. developed and carried out analysis; A.Kr., B.M.A. and P.J.H. provided theoretical guidance; B.M.A., P.J.H. and J.C.S.D. supervised the project and wrote the paper with key contributions from A.Ko., Y.X.C., P.O.S., A.Kr, and P.J.H. The manuscript reflects the contributions and ideas of all authors.

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Correspondence to J. C. Séamus Davis.

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Supplementary information

Supplementary Information

Supplementary Text, Supplementary Figures 1–22, Supplementary Video Captions 1–5, Supplementary References 1–18

Supplementary Video 1

Simulation of quasiparticle interference patterns assuming a fully coherent band structure. Video shows from energy E = –25meV to E = 25 meV in 1.25 meV steps.

Supplementary Video 2

Simulation of quasiparticle interference patterns assuming orbitally selective quasiparticle weights. Video shows from energy E = –25 meV to E = 25 meV in 1.25 meV steps.

Supplementary Video 3

Measured quasiparticle interference pattern. Video shows from energy E = –25 meV to E = 25 meV in 1.25 meV steps.

Supplementary Video 4

Measured quasiparticle interference pattern in real space within –35 meV to +35 meV energy range acquired with 1 meV spacing at 4.2 K (<TC) and 10 K (>TC).

Supplementary Video 5

Video contains real space simulated and measured quasiparticle interference pattern within –25 meV to +25 meV energy range acquired with 1.25 meV spacing.

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Kostin, A., Sprau, P.O., Kreisel, A. et al. Imaging orbital-selective quasiparticles in the Hund’s metal state of FeSe. Nature Mater 17, 869–874 (2018). https://doi.org/10.1038/s41563-018-0151-0

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