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Magnon-polarons in the Fermi–Hubbard model

Nature Physics (2025)Cite this article

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Abstract

The interplay of magnetic excitations and itinerant charge carriers is a ubiquitous phenomenon in strongly correlated electron systems. A key theoretical question is understanding the renormalization of the magnon quasiparticle, a collective spin excitation, upon doping a magnetic insulator. Here we observe a new type of quasiparticle—a magnon-Fermi-polaron—arising from the dressing of a magnon with the doped holes of a cold-atom Fermi–Hubbard system. Using Raman excitation with controlled momentum in a doped, spin-polarized band insulator, we address the spectroscopic properties of the magnon-polaron. In an undoped system with strong interactions, photoexcitation produces magnons, whose properties are accurately described by spin-wave theory. We measure the evolution of the photoexcitation spectra as we move away from this limit to produce magnon-polarons due to dressing of the magnons by charge excitations. We observe a shift in the polaron energy with doping that is strongly dependent on the injected momentum, accompanied by a reduction of spectral weight in the probed energy window. We anticipate that the technique introduced here, which is the analogue of inelastic neutron scattering, will provide atomic quantum simulators with access to the dynamics of a wide variety of excitations in strongly correlated phases.

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Fig. 1: Raman spectroscopy of a Fermi–Hubbard system.
Fig. 2: Interaction dependence of the quasiparticle energy.
Fig. 3: Doping dependence of the magnon-polaron energy.
Fig. 4: Magnon-polaron dispersion and effective mass.

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Data availability

The experimental data are available from the corresponding author upon reasonable request. Source data are provided with this paper.

Code availability

The relevant codes for this work are available from the corresponding author upon reasonable request.

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Acknowledgements

We thank L. Cheuk for helpful discussions, and A. Hasan for assistance in early stages of this work. The experimental work was supported by the NSF (grant no. 2110475 and QLCI grant no. OMA-2120757), the David and Lucile Packard Foundation (grant no. 2016-65128) and the ONR (grant no. N00014-21-1-2646). M.L.P. was supported by the NSF Graduate Research Fellowship Program. D.A.H. was supported in part by NSF QLCI grant no. OMA-2120757. I.M. and E.D. were supported by the SNSF (project 200021_212899), the Swiss State Secretariat for Education, Research and Innovation (contract number UeM019-1) and the ARO (grant no. W911NF-20-1-0163).

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Authors and Affiliations

  1. Department of Physics, Princeton University, Princeton, NJ, USA

    Max L. Prichard, Zengli Ba, Benjamin M. Spar, David A. Huse & Waseem S. Bakr

  2. Institute for Theoretical Physics, ETH Zürich, Zurich, Switzerland

    Ivan Morera & Eugene Demler

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  1. Max L. Prichard
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Contributions

M.L.P., Z.B. and B.M.S. performed the experiments and analysed the data. W.S.B. conceived the study and supervised the experiment. I.M., E.D. and D.A.H. developed the theory. I.M. performed the numerical calculations. All authors contributed to writing the paper.

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Correspondence to Waseem S. Bakr.

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Nature Physics thanks Ariel Sommer and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary text, Figs. 1–5 and refs. 1–12.

Source data

Source Data Fig. 1

Data for experimental axes (1d,e).

Source Data Fig. 2

Data for experimental axes (2a–c).

Source Data Fig. 3

Data for experimental axes (3a,b,d,e).

Source Data Fig. 4

Data for experimental axes (4c and inset).

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Prichard, M.L., Ba, Z., Morera, I. et al. Magnon-polarons in the Fermi–Hubbard model. Nat. Phys. (2025). https://doi.org/10.1038/s41567-025-03004-6

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