Continuum of quantum fluctuations in a three-dimensional S = 1 Heisenberg magnet
Conventional crystalline magnets are characterized by symmetry breaking and normal modes of excitation called magnons, with quantized angular momentum ħ . Neutron scattering correspondingly features extra magnetic Bragg diffraction at low temperatures and dispersive inelastic scattering associated w...
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Published in | Nature physics Vol. 15; no. 1; pp. 54 - 59 |
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Main Authors | , , , , , , , , , |
Format | Journal Article |
Language | English |
Published |
London
Nature Publishing Group UK
01.01.2019
Nature Publishing Group Nature Publishing Group (NPG) |
Subjects | |
Online Access | Get full text |
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Summary: | Conventional crystalline magnets are characterized by symmetry breaking and normal modes of excitation called magnons, with quantized angular momentum
ħ
. 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
ħ
/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
2
F
7
. We show that despite the complication of random Na
1+
–Ca
2+
charge disorder, NaCaNi
2
F
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
2
F
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.
Despite of the charge disorder, the three-dimensional antiferromagnet NaCaNi
2
F
7
is an almost ideal realization of the spin-1 antiferromagnetic Heisenberg model on a pyrochlore lattice, showing key features of quantum spin liquid. |
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Bibliography: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 USDOE AC05-00OR22725 K.W.P., A.S., B.W., J.A.R. and Y.Q. performed the neutron scattering experiments. K.W.P. performed the specific heat measurements and analysed all experimental data. J.W.K. and R.J.C. synthesized and characterized the single-crystal sample. H.J.C and S.Z. performed Monte Carlo simulations and self-consistent Gaussian approximation calculations, along with assisting with the theoretical interpretation. K.W.P., C.L.B. and H.J.C. wrote the manuscript with input from all co-authors. C.L.B. oversaw all aspects of the project. Author contributions |
ISSN: | 1745-2473 1745-2481 |
DOI: | 10.1038/s41567-018-0317-3 |