Abstract

Condensed-matter analogues of the Higgs boson in particle physics allow insights into its behaviour in different symmetries and dimensionalities1. Evidence for the Higgs mode has been reported in a number of different settings, including ultracold atomic gases2, disordered superconductors3, and dimerized quantum magnets4. However, decay processes of the Higgs mode (which are eminently important in particle physics) have not yet been studied in condensed matter due to the lack of a suitable material system coupled to a direct experimental probe. A quantitative understanding of these processes is particularly important for low-dimensional systems, where the Higgs mode decays rapidly and has remained elusive to most experimental probes. Here, we discover and study the Higgs mode in a two-dimensional antiferromagnet using spin-polarized inelastic neutron scattering. Our spin-wave spectra of Ca2RuO4 directly reveal a well-defined, dispersive Higgs mode, which quickly decays into transverse Goldstone modes at the antiferromagnetic ordering wavevector. Through a complete mapping of the transverse modes in the reciprocal space, we uniquely specify the minimal model Hamiltonian and describe the decay process. We thus establish a novel condensed-matter platform for research on the dynamics of the Higgs mode.

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Acknowledgements

We acknowledge financial support from the German Science Foundation (DFG) via the coordinated research programme SFB-TRR80, and from the European Research Council via Advanced Grant 669550 (Com4Com). The experiments at Oak Ridge National Laboratory’s Spallation Neutron Source were sponsored by the Division of Scientific User Facilities, US DOE Office of Basic Energy Sciences. J.C. was supported by GACR (project no. GJ15-14523Y) and by MSMT CR under NPU II project CEITEC 2020 (LQ1601).

Author information

Author notes

    • A. Jain
    • , M. Krautloher
    •  & J. Porras

    These authors contributed equally to this work.

    • G. H. Ryu

    Present address: Max-Planck-Institute for Chemical Physics of Solids, Nöthnitzerstraße 40, D-01187 Dresden, Germany.

Affiliations

  1. Max Planck Institute for Solid State Research, Heisenbergstraße 1, D-70569 Stuttgart, Germany

    • A. Jain
    • , M. Krautloher
    • , J. Porras
    • , G. H. Ryu
    • , D. P. Chen
    • , G. Khaliullin
    • , B. Keimer
    •  & B. J. Kim
  2. Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai 400085, India

    • A. Jain
  3. Quantum Condensed Matter Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA

    • D. L. Abernathy
  4. Heinz Maier-Leibnitz Zentrum, TU München, Lichtenbergstraße 1, D-85747 Garching, Germany

    • J. T. Park
  5. Institut Laue-Langevin 6, rue Jules Horowitz, BP 156, 38042 Grenoble Cedex 9, France

    • A. Ivanov
  6. Central European Institute of Technology, Masaryk University, Kotlářská 2, 61137 Brno, Czech Republic

    • J. Chaloupka
  7. Department of Physics, Pohang University of Science and Technology, Pohang 790-784, Republic of Korea

    • B. J. Kim

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Contributions

M.K., G.H.R. and D.P.C. grew the single crystals. A.J., M.K. and J.P. characterized and co-aligned the crystals. A.J., M.K., J.P. and B.J.K. performed INS experiments and analysed the data. D.L.A., J.T.P. and A.I. supported the INS experiments. G.K. developed the theoretical model. J.C. and B.J.K. performed the numerical calculations. B.J.K. wrote the manuscript with contributions from G.K., J.C., B.K., J.P., A.J. and M.K. and discussions with all authors. B.J.K. and B.K. managed the project.

Competing interests

The authors declare no competing financial interests.

Corresponding authors

Correspondence to B. Keimer or B. J. Kim.

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DOI

https://doi.org/10.1038/nphys4077

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