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Title: Continuum of quantum fluctuations in a three-dimensional S=1 Heisenberg magnet

Abstract

Conventional crystalline magnets are characterized by symmetry breaking and normal modes of excitation called magnons, with quantized angular momentum $$\hbar$$. Neutron scattering correspondingly features extra magnetic Bragg diffraction at low temperatures and dispersive inelastic scattering associated with single magnon creation and annihilation. Exceptions are anticipated in so-called quantum spin liquids, as exemplified by the one-dimensional spin-1/2 chain, which has no magnetic order and where magnons accordingly fractionalize into spinons with angular momentum $$\hbar$$/2. This is spectacularly revealed by a continuum of inelastic neutron scattering associated with two-spinon processes. Here, we report evidence for these key features of a quantum spin liquid in the three-dimensional antiferromagnet NaCaNi 2F 7. We show that despite the complication of random Na 1+–Ca 2+ charge disorder, NaCaNi 2F 7 is an almost ideal realization of the spin-1 antiferromagnetic Heisenberg model on a pyrochlore lattice. Magnetic Bragg diffraction is absent and 90% of the neutron spectral weight forms a continuum of magnetic scattering with low-energy pinch points, indicating NaCaNi 2F 7 is in a Coulomb-like phase. Our results demonstrate that disorder can act to freeze only the lowest-energy magnetic degrees of freedom; at higher energies, a magnetic excitation continuum characteristic of fractionalized excitations persists.

Authors:
ORCiD logo [1];  [1];  [1];  [1];  [2];  [3];  [4];  [5];  [2];  [6]
  1. Johns Hopkins Univ., Baltimore, MD (United States)
  2. Princeton Univ., NJ (United States). Dept. of Chemistry
  3. National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States). Center for Neutron Research; Univ. of Maryland, College Park, MD (United States). Dept. of Materials Science and Engineering
  4. National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States). Center for Neutron Research
  5. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  6. Johns Hopkins Univ., Baltimore, MD (United States); National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States). Center for Neutron Research; Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1559715
Grant/Contract Number:  
AC05-00OR22725
Resource Type:
Accepted Manuscript
Journal Name:
Nature Physics
Additional Journal Information:
Journal Volume: 15; Journal Issue: 1; Journal ID: ISSN 1745-2473
Publisher:
Nature Publishing Group (NPG)
Country of Publication:
United States
Language:
English

Citation Formats

Plumb, K. W., Changlani, Hitesh J., Scheie, A., Zhang, Shu, Krizan, J. W., Rodriguez-Rivera, J. A., Qiu, Yiming, Winn, B., Cava, R. J., and Broholm, C. L. Continuum of quantum fluctuations in a three-dimensional S=1 Heisenberg magnet. United States: N. p., 2018. Web. doi:10.1038/s41567-018-0317-3.
Plumb, K. W., Changlani, Hitesh J., Scheie, A., Zhang, Shu, Krizan, J. W., Rodriguez-Rivera, J. A., Qiu, Yiming, Winn, B., Cava, R. J., & Broholm, C. L. Continuum of quantum fluctuations in a three-dimensional S=1 Heisenberg magnet. United States. doi:10.1038/s41567-018-0317-3.
Plumb, K. W., Changlani, Hitesh J., Scheie, A., Zhang, Shu, Krizan, J. W., Rodriguez-Rivera, J. A., Qiu, Yiming, Winn, B., Cava, R. J., and Broholm, C. L. Mon . "Continuum of quantum fluctuations in a three-dimensional S=1 Heisenberg magnet". United States. doi:10.1038/s41567-018-0317-3. https://www.osti.gov/servlets/purl/1559715.
@article{osti_1559715,
title = {Continuum of quantum fluctuations in a three-dimensional S=1 Heisenberg magnet},
author = {Plumb, K. W. and Changlani, Hitesh J. and Scheie, A. and Zhang, Shu and Krizan, J. W. and Rodriguez-Rivera, J. A. and Qiu, Yiming and Winn, B. and Cava, R. J. and Broholm, C. L.},
abstractNote = {Conventional crystalline magnets are characterized by symmetry breaking and normal modes of excitation called magnons, with quantized angular momentum $\hbar$. Neutron scattering correspondingly features extra magnetic Bragg diffraction at low temperatures and dispersive inelastic scattering associated with single magnon creation and annihilation. Exceptions are anticipated in so-called quantum spin liquids, as exemplified by the one-dimensional spin-1/2 chain, which has no magnetic order and where magnons accordingly fractionalize into spinons with angular momentum $\hbar$/2. This is spectacularly revealed by a continuum of inelastic neutron scattering associated with two-spinon processes. Here, we report evidence for these key features of a quantum spin liquid in the three-dimensional antiferromagnet NaCaNi2F7. We show that despite the complication of random Na1+–Ca2+ charge disorder, NaCaNi2F7 is an almost ideal realization of the spin-1 antiferromagnetic Heisenberg model on a pyrochlore lattice. Magnetic Bragg diffraction is absent and 90% of the neutron spectral weight forms a continuum of magnetic scattering with low-energy pinch points, indicating NaCaNi2F7 is in a Coulomb-like phase. Our results demonstrate that disorder can act to freeze only the lowest-energy magnetic degrees of freedom; at higher energies, a magnetic excitation continuum characteristic of fractionalized excitations persists.},
doi = {10.1038/s41567-018-0317-3},
journal = {Nature Physics},
number = 1,
volume = 15,
place = {United States},
year = {2018},
month = {10}
}

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