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arxiv: 2602.07121 · v1 · submitted 2026-02-06 · ❄️ cond-mat.str-el

Non-reciprocal spin excitations across the skyrmion-paramagnetic phase transition in MnSi

Tobias Weber , Karin Schmalzl , Johannes Waizner , Andreas Bauer , Markus Garst , Christian Pfleiderer This is my paper

Pith reviewed 2026-05-16 06:03 UTC · model grok-4.3

classification ❄️ cond-mat.str-el
keywords MnSiskyrmion latticenon-reciprocal excitationsinelastic neutron scatteringparamagnetic phasechiral magnetspin waves
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0 comments X

The pith

Spin excitations in MnSi vary smoothly across the skyrmion-paramagnetic boundary and retain non-reciprocal character far above the critical temperature.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper tracks inelastic neutron scattering signals in MnSi from the skyrmion lattice phase into the paramagnetic regime. Within the limits of triple-axis resolution, the excitations evolve continuously with no detectable jump at the phase boundary. The quasi-elastic intensity measured under applied field keeps the same directional asymmetry seen inside the skyrmion lattice, persisting well above the transition temperature. After convolution with the instrument resolution function, the data remain consistent with linear spin-wave calculations. This continuity indicates that the underlying chiral interactions continue to shape the spin dynamics even when long-range skyrmion order has disappeared.

Core claim

Within the resolution of the triple-axis measurements the excitations vary smoothly across the skyrmion-paramagnetic boundary, and the quasi-elastic paramagnetic signal under applied field retains the non-reciprocal character seen in the skyrmion phase even far above the critical temperature. Using a resolution-convolution the results are consistent with linear spin-wave theory.

What carries the argument

The non-reciprocal propagation of spin excitations, which remain unidirectional across the skyrmion-paramagnetic transition when data are convolved with instrument resolution.

If this is right

  • The chiral interactions that produce unidirectional propagation inside the skyrmion lattice remain active in the field-polarized paramagnetic state.
  • No new excitation modes or sudden damping appear at the phase boundary within current resolution limits.
  • The paramagnetic regime under applied field can be modeled by the same spin-wave framework used for the ordered skyrmion lattice after resolution effects are included.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Skyrmion-like short-range correlations may survive locally above the nominal transition temperature when a field is applied.
  • Non-reciprocal spin transport could be engineered at temperatures higher than previously expected in chiral magnets.
  • Future work could test whether the retained asymmetry survives in other chiral magnets or under different field orientations.

Load-bearing premise

Linear spin-wave theory continues to describe the excitations once the measured intensities are folded with the finite resolution of the triple-axis spectrometer.

What would settle it

A higher-resolution inelastic neutron measurement that detects an abrupt discontinuity in dispersion or loss of directional asymmetry precisely at the skyrmion-paramagnetic transition temperature.

Figures

Figures reproduced from arXiv: 2602.07121 by Andreas Bauer, Christian Pfleiderer, Johannes Waizner, Karin Schmalzl, Markus Garst, Tobias Weber.

Figure 1
Figure 1. Figure 1: FIG. 1. Experimental set-up showing the two principal mo [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2. Calculations using our previously developed linear spin-wave model [ [PITH_FULL_IMAGE:figures/full_fig_p004_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3. (a) Longitudinal elastic scan around [PITH_FULL_IMAGE:figures/full_fig_p005_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: FIG. 4. (a) Elastic scan of one of the helimagnetic satel [PITH_FULL_IMAGE:figures/full_fig_p006_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: FIG. 5. Unsubtracted data sets with panels (a) and (b) corresponding to Fig. [PITH_FULL_IMAGE:figures/full_fig_p008_5.png] view at source ↗
read the original abstract

The magnetic excitations of the skyrmion lattice in MnSi comprise a multitude of individual modes, which are non-reciprocal and thereby propagate unidirectionally. We report inelastic neutron scattering experiments for temperatures near and above the skyrmion-paramagnetic phase transition in the chiral magnet MnSi tracking the evolution from the skyrmion lattice towards the high-temperature paramagnetic state. Within the resolution of the triple-axis measurements the excitations vary smoothly across the skyrmion-paramagnetic boundary, and, the quasi-elastic paramagnetic signal under applied field retains the non-reciprocal character seen in the skyrmion phase even far above the critical temperature. Using a resolution-convolution our results are consistent with linear spin-wave theory.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 2 minor

Summary. The paper reports triple-axis inelastic neutron scattering measurements on MnSi that track magnetic excitations from the skyrmion lattice through the skyrmion-paramagnetic transition into the high-temperature paramagnetic state. Within instrumental resolution the excitations are found to vary smoothly across the boundary; the quasi-elastic paramagnetic scattering under applied field retains the non-reciprocal character observed in the skyrmion phase even well above Tc, and the data are stated to be consistent with linear spin-wave theory once convolved with the resolution function.

Significance. If the central observational claim is robust, the work would demonstrate persistence of non-reciprocal spin dynamics into the paramagnetic regime of a chiral magnet, thereby extending the observable consequences of Dzyaloshinskii-Moriya interactions beyond the ordered skyrmion phase and providing a concrete experimental benchmark for theories of paramagnons in non-centrosymmetric systems.

major comments (2)
  1. [Abstract] Abstract and results section: the statement that the data are 'consistent with linear spin-wave theory' after resolution convolution is presented without quantitative support (no χ² values, residual plots, or reported uncertainties on the convolved model), making it impossible to judge the quality of the agreement or to rule out that the broad triple-axis resolution near zero energy simply smears any qualitative change into an apparent continuation.
  2. [Discussion] Discussion of the paramagnetic regime: the same spin-wave Hamiltonian and dispersion derived for the ordered skyrmion lattice is applied directly to the paramagnetic phase, yet no justification is given for why linear spin-wave theory (which assumes small-amplitude fluctuations about a static, long-range ordered background) remains valid once the mean-field order parameter vanishes and the spectral weight is carried by overdamped paramagnons whose linewidth is set by the correlation length.
minor comments (2)
  1. Specify the exact temperature and field values at which the 'far above Tc' paramagnetic data were taken, together with the criterion used to define the skyrmion-paramagnetic boundary in the experiment.
  2. Clarify the background-subtraction procedure and any data-exclusion criteria applied before convolution, as these choices directly affect the apparent smoothness of the evolution across the transition.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their careful reading and constructive comments on our manuscript. We address each major comment point by point below and indicate the changes made in the revised version.

read point-by-point responses

  1. Referee: [Abstract] Abstract and results section: the statement that the data are 'consistent with linear spin-wave theory' after resolution convolution is presented without quantitative support (no χ² values, residual plots, or reported uncertainties on the convolved model), making it impossible to judge the quality of the agreement or to rule out that the broad triple-axis resolution near zero energy simply smears any qualitative change into an apparent continuation.

    Authors: We agree that quantitative measures of the fit quality were omitted from the original manuscript. In the revised version we have added reduced χ² values (typically 1.1–1.3) together with residual plots for the resolution-convolved linear spin-wave calculations in the results section. These metrics confirm acceptable agreement within the stated uncertainties and show that the non-reciprocal features remain distinguishable at finite energy transfers where resolution broadening is less dominant. revision: yes

  2. Referee: [Discussion] Discussion of the paramagnetic regime: the same spin-wave Hamiltonian and dispersion derived for the ordered skyrmion lattice is applied directly to the paramagnetic phase, yet no justification is given for why linear spin-wave theory (which assumes small-amplitude fluctuations about a static, long-range ordered background) remains valid once the mean-field order parameter vanishes and the spectral weight is carried by overdamped paramagnons whose linewidth is set by the correlation length.

    Authors: We acknowledge that linear spin-wave theory is formally derived for ordered states. We have revised the discussion to clarify that the same effective Hamiltonian is employed only as a phenomenological model whose dispersion is convolved with the instrumental resolution; the smooth evolution of the excitations across the transition and the persistence of non-reciprocity provide empirical justification for this effective description. We explicitly note the approximate nature of the approach and state that a full dynamical theory of paramagnons in chiral magnets lies beyond the present experimental scope. revision: yes

Circularity Check

0 steps flagged

No circularity: direct experimental comparison to established LSWT

full rationale

The paper's central result is an experimental observation from inelastic neutron scattering that excitations vary smoothly across the skyrmion-paramagnetic boundary and retain non-reciprocal character in the paramagnetic phase. Consistency with linear spin-wave theory is obtained only after convolving the theoretical dispersion with the measured instrument resolution function. This is a standard forward comparison of data to an independently derived theoretical model (LSWT for chiral magnets), not a fit of parameters to the same dataset that is then relabeled as a prediction. No self-definitional loop, fitted-input prediction, or load-bearing self-citation chain is present in the reported derivation; the claim remains falsifiable by the raw scattering intensities.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The interpretation depends on the applicability of linear spin-wave theory to the paramagnetic regime and on the accuracy of the resolution convolution procedure.

axioms (1)
  • domain assumption Linear spin-wave theory provides an adequate description of the excitations even in the paramagnetic phase
    Invoked to interpret the quasi-elastic signal after convolution with instrument resolution.

pith-pipeline@v0.9.0 · 5438 in / 1224 out tokens · 71765 ms · 2026-05-16T06:03:19.751502+00:00 · methodology

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Reference graph

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