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Quasiparticle breakdown in a quantum spin liquid

Author

Listed:
  • Matthew B. Stone

    (Oak Ridge National Laboratory)

  • Igor A. Zaliznyak

    (Brookhaven National Laboratory)

  • Tao Hong

    (The Johns Hopkins University)

  • Collin L. Broholm

    (The Johns Hopkins University
    National Institute of Standards and Technology)

  • Daniel H. Reich

    (The Johns Hopkins University)

Abstract

Much of modern condensed matter physics is understood in terms of elementary excitations, or quasiparticles—fundamental quanta of energy and momentum1,2. Various strongly interacting atomic systems are successfully treated as a collection of quasiparticles with weak or no interactions. However, there are interesting limitations to this description: in some systems the very existence of quasiparticles cannot be taken for granted. Like unstable elementary particles, quasiparticles cannot survive beyond a threshold where certain decay channels become allowed by conservation laws; their spectrum terminates at this threshold. Such quasiparticle breakdown was first predicted for an exotic state of matter—super-fluid 4He at temperatures close to absolute zero, a quantum Bose liquid where zero-point atomic motion precludes crystallization1,2,3,4. Here we show, using neutron scattering, that quasiparticle breakdown can also occur in a quantum magnet and, by implication, in other systems with Bose quasiparticles. We have measured spin excitations in a two-dimensional quantum magnet, piperazinium hexachlorodicuprate (PHCC)5, in which spin-1/2 copper ions form a non-magnetic quantum spin liquid, and find remarkable similarities with excitations in superfluid 4He. We observe a threshold momentum beyond which the quasiparticle peak merges with the two-quasiparticle continuum. It then acquires a finite energy width and becomes indistinguishable from a leading-edge singularity, so that excited states are no longer quasiparticles but occupy a wide band of energy. Our findings have important ramifications for understanding excitations with gapped spectra in many condensed matter systems, ranging from band insulators to high-transition-temperature superconductors6.

Suggested Citation

  • Matthew B. Stone & Igor A. Zaliznyak & Tao Hong & Collin L. Broholm & Daniel H. Reich, 2006. "Quasiparticle breakdown in a quantum spin liquid," Nature, Nature, vol. 440(7081), pages 187-190, March.
  • Handle: RePEc:nat:nature:v:440:y:2006:i:7081:d:10.1038_nature04593
    DOI: 10.1038/nature04593
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    Cited by:

    1. A. Nag & A. Nocera & S. Agrestini & M. Garcia-Fernandez & A. C. Walters & Sang-Wook Cheong & S. Johnston & Ke-Jin Zhou, 2022. "Quadrupolar magnetic excitations in an isotropic spin-1 antiferromagnet," Nature Communications, Nature, vol. 13(1), pages 1-7, December.
    2. Tao Hong & Tao Ying & Qing Huang & Sachith E. Dissanayake & Yiming Qiu & Mark M. Turnbull & Andrey A. Podlesnyak & Yan Wu & Huibo Cao & Yaohua Liu & Izuru Umehara & Jun Gouchi & Yoshiya Uwatoko & Masa, 2022. "Evidence for pressure induced unconventional quantum criticality in the coupled spin ladder antiferromagnet C9H18N2CuBr4," Nature Communications, Nature, vol. 13(1), pages 1-9, December.
    3. Xiaojian Bai & Shang-Shun Zhang & Hao Zhang & Zhiling Dun & W. Adam Phelan & V. Ovidiu Garlea & Martin Mourigal & Cristian D. Batista, 2023. "Instabilities of heavy magnons in an anisotropic magnet," Nature Communications, Nature, vol. 14(1), pages 1-11, December.
    4. Shunsuke Hasegawa & Hodaka Kikuchi & Shinichiro Asai & Zijun Wei & Barry Winn & Gabriele Sala & Shinichi Itoh & Takatsugu Masuda, 2024. "Field control of quasiparticle decay in a quantum antiferromagnet," Nature Communications, Nature, vol. 15(1), pages 1-7, December.

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