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Continuous excitations of the triangular-lattice quantum spin liquid YbMgGaO4

Nature Physics volume 13, pages 117–122 (2017)Cite this article

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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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Figure 1: Structure and magnetic properties of YbMgGaO4.
Figure 2: Neutron-scattering data for YbMgGaO4 measured in zero applied field.
Figure 3: Field-polarized neutron-scattering data and evidence for next-nearest-neighbour interactions 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

  1. Marcus Daum and Zhiling Dun: These authors contributed equally to this work.

Authors and 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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  1. Joseph A. M. Paddison
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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.

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Correspondence to Martin Mourigal.

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The authors declare no competing financial interests.

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Paddison, J., Daum, M., Dun, Z. et al. Continuous excitations of the triangular-lattice quantum spin liquid YbMgGaO4. Nature Phys 13, 117–122 (2017). https://doi.org/10.1038/nphys3971

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