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Title: Dynamic Spin Correlations in the Honeycomb Lattice Na 2 IrO 3 Measured by Resonant Inelastic x-Ray Scattering

Abstract

Kitaev quantum spin liquid is a prime example of novel quantum magnetism of spin-orbit entangled pseudospin-1/2 moments in a honeycomb lattice. Most candidate materials such as Na2IrO3 have many competing exchange interactions beyond the minimal Kitaev-Heisenberg model whose small variations in the strength of the interactions produce huge differences in low energy dynamics. An incomplete knowledge of dynamic spin correlations hampers identification of a minimal model and quantification of the proximity to the Kitaev quantum spin-liquid phase. Here, we report fully momentum- and energy-resolved magnetic excitation spectra in a honeycomb lattice Na2IrO3 measured using resonant inelastic x-ray scattering. The state-of-the-art 10 meV energy resolution spectrometer resolves a low energy quasiparticle peak but reveals that the dynamic response lacks a resolution-limited coherent spin waves in most part of the Brillouin zone. Dynamical structure factors were calculated using exact diagonalization method on finite-size clusters. The effective spin Hamiltonian contains six parameters including all symmetry-allowed nearest neighbor interactions and long-range Heisenberg interactions. Our results confine a parameter regime in which the spin Hamiltonian reasonably reproduces the measured magnetic excitation spectra in terms of spectral width and energy. A hidden Kitaev quantum spin liquid and Heisenberg phases found in the complex parameter space aremore » used as a reference to determine the Kitaev-like or magnon-like nature of the spin excitations. Magnetic excitation spectra were taken at elevated temperatures to follow temperature evolution of the RIXS dynamic response in the paramagnetic state. Whereas the low energy excitation progressively diminishes as the zigzag order disappears, the broad high energy excitation maintains its spectral weight up to much higher temperature of 160 K and diminishes only above 200 K. Finally, we discuss our results in the context of a frustrated magnet proximate to the Kitaev quantum spin liquid.« less

Authors:
ORCiD logo; ORCiD logo; ; ; ; ; ; ;
Publication Date:
Research Org.:
Argonne National Laboratory (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC); Czech Science Foundation (GA CR)
OSTI Identifier:
1618387
Alternate Identifier(s):
OSTI ID: 1618448
Grant/Contract Number:  
AC02-06CH11357
Resource Type:
Published Article
Journal Name:
Physical Review. X
Additional Journal Information:
Journal Name: Physical Review. X Journal Volume: 10 Journal Issue: 2; Journal ID: ISSN 2160-3308
Publisher:
American Physical Society (APS)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; Kitaev quantum spin liquid; resonant inelastic x-ray scattering; antiferromagnetism; magnons; spin dynamics; antiferromagnets; honeycomb lattice; Mott insulators; single crystal materials; crystal growth; exact diagnolization; liquid helium cooling

Citation Formats

Kim, Jungho, Chaloupka, Jiří, Singh, Yogesh, Kim, J. W., Kim, B. J., Casa, D., Said, A., Huang, X., and Gog, T. Dynamic Spin Correlations in the Honeycomb Lattice Na 2 IrO 3 Measured by Resonant Inelastic x-Ray Scattering. United States: N. p., 2020. Web. doi:10.1103/PhysRevX.10.021034.
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Kim, Jungho, Chaloupka, Jiří, Singh, Yogesh, Kim, J. W., Kim, B. J., Casa, D., Said, A., Huang, X., & Gog, T. Dynamic Spin Correlations in the Honeycomb Lattice Na 2 IrO 3 Measured by Resonant Inelastic x-Ray Scattering. United States. https://doi.org/10.1103/PhysRevX.10.021034
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Kim, Jungho, Chaloupka, Jiří, Singh, Yogesh, Kim, J. W., Kim, B. J., Casa, D., Said, A., Huang, X., and Gog, T. Wed . "Dynamic Spin Correlations in the Honeycomb Lattice Na 2 IrO 3 Measured by Resonant Inelastic x-Ray Scattering". United States. https://doi.org/10.1103/PhysRevX.10.021034.
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@article{osti_1618387,
title = {Dynamic Spin Correlations in the Honeycomb Lattice Na 2 IrO 3 Measured by Resonant Inelastic x-Ray Scattering},
author = {Kim, Jungho and Chaloupka, Jiří and Singh, Yogesh and Kim, J. W. and Kim, B. J. and Casa, D. and Said, A. and Huang, X. and Gog, T.},
abstractNote = {Kitaev quantum spin liquid is a prime example of novel quantum magnetism of spin-orbit entangled pseudospin-1/2 moments in a honeycomb lattice. Most candidate materials such as Na2IrO3 have many competing exchange interactions beyond the minimal Kitaev-Heisenberg model whose small variations in the strength of the interactions produce huge differences in low energy dynamics. An incomplete knowledge of dynamic spin correlations hampers identification of a minimal model and quantification of the proximity to the Kitaev quantum spin-liquid phase. Here, we report fully momentum- and energy-resolved magnetic excitation spectra in a honeycomb lattice Na2IrO3 measured using resonant inelastic x-ray scattering. The state-of-the-art 10 meV energy resolution spectrometer resolves a low energy quasiparticle peak but reveals that the dynamic response lacks a resolution-limited coherent spin waves in most part of the Brillouin zone. Dynamical structure factors were calculated using exact diagonalization method on finite-size clusters. The effective spin Hamiltonian contains six parameters including all symmetry-allowed nearest neighbor interactions and long-range Heisenberg interactions. Our results confine a parameter regime in which the spin Hamiltonian reasonably reproduces the measured magnetic excitation spectra in terms of spectral width and energy. A hidden Kitaev quantum spin liquid and Heisenberg phases found in the complex parameter space are used as a reference to determine the Kitaev-like or magnon-like nature of the spin excitations. Magnetic excitation spectra were taken at elevated temperatures to follow temperature evolution of the RIXS dynamic response in the paramagnetic state. Whereas the low energy excitation progressively diminishes as the zigzag order disappears, the broad high energy excitation maintains its spectral weight up to much higher temperature of 160 K and diminishes only above 200 K. Finally, we discuss our results in the context of a frustrated magnet proximate to the Kitaev quantum spin liquid.},
doi = {10.1103/PhysRevX.10.021034},
journal = {Physical Review. X},
number = 2,
volume = 10,
place = {United States},
year = {Wed May 13 00:00:00 EDT 2020},
month = {Wed May 13 00:00:00 EDT 2020}
}
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Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record
https://doi.org/10.1103/PhysRevX.10.021034
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Cited by: 24 works
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Figures / Tables:

FIG. 1 FIG. 1: Magnetic excitation spectra in Na2IrO3 along high-symmetry Brillouin zone directions taken at T = 7 K. (a) Scattering geometry. Yellow arrows indicate incident and scattered x rays, which define the scattering plane (gray). Brown arrows indicate x-ray polarizations. Green arrows indicate the cubic axes (x, y, z) withmore » respect to the octahedra (all of them point above the paper plane). (b) One of the collinear zigzag patterns and the corresponding direction of the ordered moments. The left-facing arrows have an out-of-plane component pointing above the paper plane; i.e., the corresponding moment direction lies approximately between the x and y axes. (c) Two-dimensional reciprocal space diagram showing the measured path along the symmetry directions. The inner hexagon (blue dashed line) indicates the first Brillouin zone of the honeycomb lattice. (d) RIXS intensity map of magnetic excitations in Na2IrO3 as functions of the wave vector and energy loss. (e) The intensity profiles integrated over [60, 105] (open squares) and [105, 135] meV (filled triangles) show that the high-energy spectral intensities are broadly peaked at the Γ point, extending up to 105 meV. (f) The intensity profile integrated over [−30, 60] meV (filled squares) shows a distinctive distribution of the spectral weight along the K-Γ-Y-K'-Γ' path. Passing through the K point, the excitation intensity rapidly increases and then decreases, which is followed by a near-constant intensity along the Γ-Y-K' path. Large intensities at the Γ and Γ' wave vectors correspond to elastic scatterings. The zero-energy loss intensity at the M point is the diffuse magnetic Bragg peak. In the used scattering geometry, the magnetic Bragg peak at the Y point is suppressed.« less
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