Quantifying thermal and driven magnon populations with femtosecond noise correlation spectroscopy
Abstract
Precise knowledge of the total number of magnons, including both coherent and incoherent (e.g. thermal) excitations, is imperative for the advancement of fundamental spin-wave physics and the development of next-generation magnonic devices. In particular, quantifying magnons is key to understanding magnon transport phenomena, the nonlinear regime, or ultrafast magnetization dynamics. Typically, incoherent magnons are accessed by frequency-domain techniques, which lack the temporal resolution required for ultrafast processes, while ultrafast time-domain methods are generally sensitive only to the coherent dynamics. In this work, we demonstrate that femtosecond noise correlation spectroscopy enables a fully quantitative, time-domain measurement of both thermal and coherently excited magnon modes in bismuth-substituted yttrium iron garnet driven by a free-running microwave. We model the experimental data and extract the magnon number by simulating the magnon band structure of the sample, the magneto-optical response function, and the optical spot size used in the experiment. Our analysis establishes a connection between magnon mode calculations and experimentally accessible magnetic properties and fiducially reproduces the waveform and amplitude of the magneto-optical correlation signal for different experimental conditions. These results open a new pathway towards the optical tomography of magnon modes in non-linear or non-equilibrium conditions and can be readily extended to study ultrafast incoherent dynamics in other condensed matter systems.
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BibTeX
@misc{herbst2026quantifying,
title = {{Quantifying thermal and driven magnon populations with femtosecond noise correlation spectroscopy}},
author = {F. S. Herbst and M. A. Weiss and A. Leitenstorfer and M. Lammel and N. Beaulieu and J. Ben Youssef and R. Schlitz and S. T. B. Goennenwein},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.07421},
eprint = {2609.07421},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.07421},
note = {CC BY-NC-ND 4.0},
}
RIS
TY - UNPB
TI - Quantifying thermal and driven magnon populations with femtosecond noise correlation spectroscopy
AU - F. S. Herbst
AU - M. A. Weiss
AU - A. Leitenstorfer
AU - M. Lammel
AU - N. Beaulieu
AU - J. Ben Youssef
AU - R. Schlitz
AU - S. T. B. Goennenwein
PY - 2026
DA - 2026/09/07
PB - arXiv
DO - 10.48550/arxiv.2609.07421
UR - https://arxiv.org/abs/2609.07421
AB - Precise knowledge of the total number of magnons, including both coherent and incoherent (e.g. thermal) excitations, is imperative for the advancement of fundamental spin-wave physics and the development of next-generation magnonic devices. In particular, quantifying magnons is key to understanding magnon transport phenomena, the nonlinear regime, or ultrafast magnetization dynamics. Typically, incoherent magnons are accessed by frequency-domain techniques, which lack the temporal resolution required for ultrafast processes, while ultrafast time-domain methods are generally sensitive only to the coherent dynamics. In this work, we demonstrate that femtosecond noise correlation spectroscopy enables a fully quantitative, time-domain measurement of both thermal and coherently excited magnon modes in bismuth-substituted yttrium iron garnet driven by a free-running microwave. We model the experimental data and extract the magnon number by simulating the magnon band structure of the sample, the magneto-optical response function, and the optical spot size used in the experiment. Our analysis establishes a connection between magnon mode calculations and experimentally accessible magnetic properties and fiducially reproduces the waveform and amplitude of the magneto-optical correlation signal for different experimental conditions. These results open a new pathway towards the optical tomography of magnon modes in non-linear or non-equilibrium conditions and can be readily extended to study ultrafast incoherent dynamics in other condensed matter systems.
ER -