Nonlinear soliton confinement in weakly coupled antiferromagnetic spin chains
Abstract
In this work, we analyze the low-energy dynamics of quasi-one-dimensional, large-$$\textit{S}$$ quantum antiferromagnets with easy-axis anisotropy, using a semiclassical nonlinear sigma model. The saddle point approximation leads to a sine-Gordon equation which supports soliton solutions. These correspond to the movement of spatially extended domain walls. Long-range magnetic order is a consequence of a weak interchain coupling. Below the ordering temperature, the coupling to nearby chains leads to an energy cost associated with the separation of two domain walls. From the kink-antikink two-soliton solution, we compute the effective confinement potential. At distances large compared to the size of the solitons the potential is linear, as expected for pointlike domain walls. At small distances the gradual annihilation of the solitons weakens the effective attraction and renders the potential quadratic. From numerically solving the effective one-dimensional Schrödinger equation with this nonlinear confinement potential we compute the soliton bound state spectrum. We apply the theory to CaFe2O4, an anisotropic $$\textit{S}$$ = 5/2 magnet based upon antiferromagnetic zigzag chains. Using inelastic neutron scattering, we are able to resolve seven discrete energy levels for spectra recorded slightly below the Néel temperature $$T_N$$ ≈ 200 K. These modes are well described by our nonlinear confinement model in the regime of large spatially extended solitons.
- Authors:
-
- Univ. of Edinburgh, Scotland (United Kingdom); Science and Technology Facilities Council (STFC), Oxford (United Kingdom). Rutherford Appleton Lab. (RAL)
- Univ. of Edinburgh, Scotland (United Kingdom)
- Rutgers Univ., Piscataway, NJ (United States)
- Science and Technology Facilities Council (STFC), Oxford (United Kingdom). Rutherford Appleton Lab. (RAL)
- Science and Technology Facilities Council (STFC), Oxford (United Kingdom). Rutherford Appleton Lab. (RAL); Univ. College London (United Kingdom)
- Publication Date:
- Research Org.:
- Rutgers Univ., Piscataway, NJ (United States)
- Sponsoring Org.:
- USDOE Office of Science (SC); Engineering and Physical Sciences Research Council (EPSRC); Science and Technology Facilities Council (STFC)
- OSTI Identifier:
- 1800461
- Grant/Contract Number:
- FG02-07ER46382; EP/P013449/1
- Resource Type:
- Accepted Manuscript
- Journal Name:
- Physical Review. B
- Additional Journal Information:
- Journal Volume: 102; Journal Issue: 2; Journal ID: ISSN 2469-9950
- Publisher:
- American Physical Society (APS)
- Country of Publication:
- United States
- Language:
- English
- Subject:
- 75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; Materials Science; Physics
Citation Formats
Lane, H., Stock, C., Cheong, S.-W., Demmel, F., Ewings, R. A., and Krüger, F. Nonlinear soliton confinement in weakly coupled antiferromagnetic spin chains. United States: N. p., 2020.
Web. doi:10.1103/physrevb.102.024437.
Lane, H., Stock, C., Cheong, S.-W., Demmel, F., Ewings, R. A., & Krüger, F. Nonlinear soliton confinement in weakly coupled antiferromagnetic spin chains. United States. https://doi.org/10.1103/physrevb.102.024437
Lane, H., Stock, C., Cheong, S.-W., Demmel, F., Ewings, R. A., and Krüger, F. Wed .
"Nonlinear soliton confinement in weakly coupled antiferromagnetic spin chains". United States. https://doi.org/10.1103/physrevb.102.024437. https://www.osti.gov/servlets/purl/1800461.
@article{osti_1800461,
title = {Nonlinear soliton confinement in weakly coupled antiferromagnetic spin chains},
author = {Lane, H. and Stock, C. and Cheong, S.-W. and Demmel, F. and Ewings, R. A. and Krüger, F.},
abstractNote = {In this work, we analyze the low-energy dynamics of quasi-one-dimensional, large-$\textit{S}$ quantum antiferromagnets with easy-axis anisotropy, using a semiclassical nonlinear sigma model. The saddle point approximation leads to a sine-Gordon equation which supports soliton solutions. These correspond to the movement of spatially extended domain walls. Long-range magnetic order is a consequence of a weak interchain coupling. Below the ordering temperature, the coupling to nearby chains leads to an energy cost associated with the separation of two domain walls. From the kink-antikink two-soliton solution, we compute the effective confinement potential. At distances large compared to the size of the solitons the potential is linear, as expected for pointlike domain walls. At small distances the gradual annihilation of the solitons weakens the effective attraction and renders the potential quadratic. From numerically solving the effective one-dimensional Schrödinger equation with this nonlinear confinement potential we compute the soliton bound state spectrum. We apply the theory to CaFe2O4, an anisotropic $\textit{S}$ = 5/2 magnet based upon antiferromagnetic zigzag chains. Using inelastic neutron scattering, we are able to resolve seven discrete energy levels for spectra recorded slightly below the Néel temperature $T_N$ ≈ 200 K. These modes are well described by our nonlinear confinement model in the regime of large spatially extended solitons.},
doi = {10.1103/physrevb.102.024437},
journal = {Physical Review. B},
number = 2,
volume = 102,
place = {United States},
year = {Wed Jul 22 00:00:00 EDT 2020},
month = {Wed Jul 22 00:00:00 EDT 2020}
}
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