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Bond-dependent anisotropy and magnon decay in cobalt-based Kitaev triangular antiferromagnet

Nature Physics volume 19, pages 1624–1629 (2023)Cite this article

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Abstract

The Kitaev model, a honeycomb network of spins with bond-dependent anisotropic interactions, is a rare example of a system with a quantum spin liquid ground state. Although most Kitaev model candidate materials eventually order magnetically due to additional non-Kitaev interactions, their bond-dependent anisotropy manifests in unusual spin dynamics. Recent research suggests that bond-dependent anisotropy can stabilize exotic magnetic phases on the geometrically frustrated triangular lattice. Unfortunately, few materials have been identified with simultaneous geometric frustration and bond-dependent anisotropy. Here, we report a frustrated triangular lattice with bond-dependent anisotropy in the cobalt-based van der Waals antiferromagnet CoI2. Momentum and energy-resolved inelastic neutron scattering measurements show substantial magnon decay and level repulsion. A thorough examination of excitations in both the paramagnetic and magnetically ordered states demonstrates that the bond-dependent anisotropy is the origin of the spiral order and the magnon decay found in CoI2. Our results provide the basis for future studies of the interplay between Kitaev magnetism and geometric frustration.

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Fig. 1: Schematic view of Kitaev model, spin-orbital entangled Jeff = 1/2 state, spiral magnetic structure and magnetic phase diagram of CoI2.
Fig. 2: Diffuse and inelastic scattering in the paramagnetic regime of CoI2.
Fig. 3: Spin-wave excitations and magnon decay in magnetically ordered CoI2.
Fig. 4: Two-magnon DOS, magnon decay and selective avoided decay mode.

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The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request. Source data are provided with this paper.

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The source code used in this study is available from the corresponding author upon reasonable request.

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Acknowledgements

We thank P. Maksimov, K. Barros, M. Willson and C. D. Batista for fruitful discussions. This work was supported by the Leading Researcher Program of the National Research Foundation of Korea (Grant No. 2020R1A3B2079375). The INS experiment was performed at the MLF of J-PARC under a user program (Proposal No. 2020B0407). The work of A.L.C. was supported by the US Department of Energy, Office of Science, Basic Energy Sciences under Award No. DE-SC0021221. The work of M.M. was supported by the US Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division under award DE-SC-0018660. The work of S.K. and S.-J.K was supported by the Pioneer Research Center Program through the National Research Foundation of Korea funded by the Ministry of Science, ICT & Future Planning (NRF-2022M3C1A309198811).

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Author notes

  1. These authors contributed equally: Chaebin Kim, Sujin Kim.

Authors and Affiliations

  1. Center for Quantum Materials, Seoul National University, Seoul, Republic of Korea

    Chaebin Kim, Pyeongjae Park, Taehun Kim, Jaehong Jeong & Je-Geun Park

  2. Department of Physics and Astronomy, Seoul National University, Seoul, Republic of Korea

    Chaebin Kim, Pyeongjae Park, Taehun Kim, Jaehong Jeong & Je-Geun Park

  3. Department of Chemistry and Nano Science, Ewha Womans University, Seoul, Republic of Korea

    Sujin Kim & Sung-Jin Kim

  4. Materials and Life Science Division, J-PARC Center, Tokai, Japan

    Seiko Ohira-Kawamura, Naoki Murai & Kenji Nakajima

  5. Department of Physics and Astronomy, University of California, Irvine, CA, USA

    A. L. Chernyshev

  6. School of Physics, Georgia Institute of Technology, Atlanta, GA, USA

    Martin Mourigal

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Contributions

J.-G.P. initiated and supervised the project. S.K., C.K. and S.-J.K. grew the single crystal using the Bridgman furnace. C.K. aligned the sample for measurements. S.O.-K., N.M., C.K., P.P., T.K., J.-G.P. and K.N. performed the INS measurement. C.K. analysed the data and performed an LSWT calculation. C.K. and M.M. performed the LLD simulations. P.P., M.M. and A.L.C. contributed to the theoretical interpretation and discussion. C.K., M.M. and J.-G.P. wrote the manuscript with input from all authors.

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Correspondence to Je-Geun Park.

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Supplementary Discussion, Figs. 1–13 and Table 1.

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Statistical source data of Fig. 4d,e.

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Kim, C., Kim, S., Park, P. et al. Bond-dependent anisotropy and magnon decay in cobalt-based Kitaev triangular antiferromagnet. Nat. Phys. 19, 1624–1629 (2023). https://doi.org/10.1038/s41567-023-02180-7

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