Multimagnon bound states in the polarized phase of anisotropic antiferromagnets
Abstract
We investigate single-ion bound magnon states in the high-field polarized phase of uniaxial antiferromagnets. By solving the two-particle problem exactly, we determine the dispersion of bound magnon pairs both below and above the continuum. We also obtain rigorous bounds on their binding energies by using the Gershgorin circle theorem. For spin-1 easy-axis systems, two-magnon bound states with zero total momentum emerge as low-energy excitations once the ratio of single-ion anisotropy to exchange exceeds a threshold value. As the field decreases, magnon pairs condense, driving a transition into a spin-nematic phase. Beyond the two-magnon problem, we develop a general strong-coupling approach that describes n-magnon single-ion bound states (n≤ 2S) in large-S easy-axis antiferromagnets. The Bose-Einstein condensation of these multi-magnon excitations yields a rich hierarchy of field-induced multipolar phases stabilized by single-ion anisotropy. Comparisons with recent experiments on Na2BaNi(PO4)2 and Sr2CoGe2O7 illustrate the quantitative power of our theory.
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BibTeX
@misc{mendili2026multimagnon,
title = {{Multimagnon bound states in the polarized phase of anisotropic antiferromagnets}},
author = {A. El Mendili and M. E. Zhitomirsky},
howpublished = {arXiv},
year = {2026},
month = nov,
doi = {10.48550/arxiv.2611.08349},
eprint = {2611.08349},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2611.08349},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Multimagnon bound states in the polarized phase of anisotropic antiferromagnets
AU - A. El Mendili
AU - M. E. Zhitomirsky
PY - 2026
DA - 2026/11/05
PB - arXiv
DO - 10.48550/arxiv.2611.08349
UR - https://arxiv.org/abs/2611.08349
AB - We investigate single-ion bound magnon states in the high-field polarized phase of uniaxial antiferromagnets. By solving the two-particle problem exactly, we determine the dispersion of bound magnon pairs both below and above the continuum. We also obtain rigorous bounds on their binding energies by using the Gershgorin circle theorem. For spin-1 easy-axis systems, two-magnon bound states with zero total momentum emerge as low-energy excitations once the ratio of single-ion anisotropy to exchange exceeds a threshold value. As the field decreases, magnon pairs condense, driving a transition into a spin-nematic phase. Beyond the two-magnon problem, we develop a general strong-coupling approach that describes n-magnon single-ion bound states (n≤ 2S) in large-S easy-axis antiferromagnets. The Bose-Einstein condensation of these multi-magnon excitations yields a rich hierarchy of field-induced multipolar phases stabilized by single-ion anisotropy. Comparisons with recent experiments on Na_2BaNi(PO_4)_2 and Sr_2CoGe_2O_7 illustrate the quantitative power of our theory.
ER -