Non-equilibrium Muon Dynamics Imitating Fractional Spin Excitations in a Quantum Spin Chain
Abstract
Fractional spin excitations in low-dimensional and frustrated magnets are commonly associated with sporadic spin fluctuations, as observed in quantum spin liquids, spin ices, and other complex magnetic states. In this study, we investigate the spin dynamics in the amplitude-modulated magnetic ground state of AgCuVO4, a spin-1/2 chain compound with competing intrachain interactions, by muon spectroscopy. Our data reveal a Gaussian decay of muon polarization that remains remarkably resilient against applied magnetic fields---a behavior often interpreted as evidence of emergent sporadic spin dynamics. However, density functional theory calculations of muon stopping sites and their quadrupolar level-crossing resonance spectra suggest an alternative mechanism: a two-state model where the muon randomly hops between two nearby sites, eventually equilibrating across both on a microsecond timescale via quantum delocalization. These findings provide a microscopic explanation for the field-resilient muon polarization and indicate that such behavior may not always stem from intrinsic spin fluctuations, but can also arise from non-equilibrium muon dynamics.
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BibTeX
@misc{hromov2026nonequilibrium,
title = {{Non-equilibrium Muon Dynamics Imitating Fractional Spin Excitations in a Quantum Spin Chain}},
author = {A. Hromov and A. Zorko and M. Gomilšek and P. J. Baker and A. Prokofiev and M. Pregelj},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.21523},
eprint = {2610.21523},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.21523},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Non-equilibrium Muon Dynamics Imitating Fractional Spin Excitations in a Quantum Spin Chain
AU - A. Hromov
AU - A. Zorko
AU - M. Gomilšek
AU - P. J. Baker
AU - A. Prokofiev
AU - M. Pregelj
PY - 2026
DA - 2026/10/15
PB - arXiv
DO - 10.48550/arxiv.2610.21523
UR - https://arxiv.org/abs/2610.21523
AB - Fractional spin excitations in low-dimensional and frustrated magnets are commonly associated with sporadic spin fluctuations, as observed in quantum spin liquids, spin ices, and other complex magnetic states. In this study, we investigate the spin dynamics in the amplitude-modulated magnetic ground state of AgCuVO_4, a spin-1/2 chain compound with competing intrachain interactions, by muon spectroscopy. Our data reveal a Gaussian decay of muon polarization that remains remarkably resilient against applied magnetic fields---a behavior often interpreted as evidence of emergent sporadic spin dynamics. However, density functional theory calculations of muon stopping sites and their quadrupolar level-crossing resonance spectra suggest an alternative mechanism: a two-state model where the muon randomly hops between two nearby sites, eventually equilibrating across both on a microsecond timescale via quantum delocalization. These findings provide a microscopic explanation for the field-resilient muon polarization and indicate that such behavior may not always stem from intrinsic spin fluctuations, but can also arise from non-equilibrium muon dynamics.
ER -