Abstract

A quantum spin liquid (QSL) is an exotic state of matter in which electrons’ spins are quantum entangled over long distances, but do not show magnetic order in the zero-temperature limit1. The observation of QSL states is a central aim of experimental physics, because they host collective excitations that transcend our knowledge of quantum matter; however, examples in real materials are scarce2. Here, we report neutron-scattering experiments on YbMgGaO4, a QSL candidate in which Yb3+ ions with effective spin-1/2 occupy a triangular lattice3,4,5,6. Our measurements reveal a continuum of magnetic excitations—the essential experimental hallmark of a QSL7—at very low temperature (0.06 K). The origin of this peculiar excitation spectrum is a crucial question, because isotropic nearest-neighbour interactions do not yield a QSL ground state on the triangular lattice8. Using measurements in the field-polarized state, we identify antiferromagnetic next-nearest-neighbour interactions9,10,11,12, spin-space anisotropies4,10,13,14, and chemical disorder15 between the magnetic layers as key ingredients in YbMgGaO4.

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Acknowledgements

We are very grateful to L. Ge for his help with heat-capacity measurements and J. Carruth, S. Elorfi, M. Everett and C. Fletcher for sample environment and instrument support during our neutron-scattering experiments. It is our pleasure to thank S. Chernyshev, R. Coldea, K. Ross, M. Waterbury, Y. Wan and M. Zhitomirsky for insightful discussions. The work and equipment at the Georgia Institute of Technology (J.A.M.P., M.D. and M.M.) was supported by the College of Sciences and the Executive Vice-President for Research. The work at the University of Tennessee (Z.D. and H.Z.) was supported by the National Science Foundation through award DMR-1350002. The research at Oak Ridge National Laboratory’s Spallation Neutron Source was sponsored by the US Department of Energy, Office of Basic Energy Sciences, Scientific User Facilities Division.

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Author notes

    • Marcus Daum
    •  & Zhiling Dun

    These authors contributed equally to this work.

Affiliations

  1. School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332, USA

    • Joseph A. M. Paddison
    • , Marcus Daum
    •  & Martin Mourigal
  2. Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996, USA

    • Zhiling Dun
    •  & Haidong Zhou
  3. Quantum Condensed Matter Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA

    • Georg Ehlers
    • , Yaohua Liu
    •  & Matthew B. Stone

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Contributions

J.A.M.P., M.D., Z.D., G.E., Y.L., M.B.S. and M.M. performed neutron-scattering experiments. J.A.M.P., M.D. and M.M. analysed the data. Z.D. and H.Z. made the sample. Z.D. and M.M. characterized the sample. M.D. and M.M. aligned the sample. M.M. made the figures and J.A.M.P. wrote the paper with input from all authors. H.Z. and M.M. designed and supervised the project.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Martin Mourigal.

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https://doi.org/10.1038/nphys3971

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