SciPost Submission Page
Interaction and collision of skyrmions in chiral antiferromagnets
by George Theodorou, Bruno Barton-Singer, Stavros Komineas
Submission summary
| Authors (as registered SciPost users): | Stavros Komineas |
| Submission information | |
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| Preprint Link: | https://arxiv.org/abs/2305.13515v2 (pdf) |
| Date submitted: | 2024-10-04 11:47 |
| Submitted by: | Komineas, Stavros |
| Submitted to: | SciPost Physics |
| Ontological classification | |
|---|---|
| Academic field: | Physics |
| Specialties: |
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| Approaches: | Theoretical, Computational |
Abstract
Skyrmions in an antiferromagnet can travel as solitary waves in stark contrast to the situation in ferromagnets. Traveling skyrmion solutions have been found numerically in chiral antiferromagnets. We study head-on collision events between two skyrmions. We find that the result of the collision depends on the initial velocity of the skyrmions. For small velocities, the skyrmions shrink as they approach, then bounce back and eventually acquire almost their initial speed. For larger velocities, the skyrmions approach each other and shrink until they become singular points at some finite separation and are eventually annihilated. Considering skyrmion energetics, we can determine the regimes of the different dynamical behaviors. Using a collective co-ordinate approach, we reproduce the dynamics of the collisions including the variation of the size of the skyrmions and collapse above a critical velocity.
Author indications on fulfilling journal expectations
- Provide a novel and synergetic link between different research areas.
- Open a new pathway in an existing or a new research direction, with clear potential for multi-pronged follow-up work
- Detail a groundbreaking theoretical/experimental/computational discovery
- Present a breakthrough on a previously-identified and long-standing research stumbling block
Author comments upon resubmission
In the resubmission, the manuscript has been completed extensively in a very significant way, where a colleague (who is now a co-author) has made the central contributions. We have added a Section (4) for the understanding of skyrmion scattering via a collective co-ordinate approach. This shows the origin of the scale change of skyrmions during scattering and the role that it plays in the dynamics. Virtually all significant features of the collision dynamics are now discussed in detail. The collective co-ordinate dynamics faithfully reproduces the full-field (simulation) results.
The theoretical approach involves results from soliton theory and from field theories outside magnetism or condensed matter. This is reflected in the list of references (e.g., in Section 4). It demonstrates in a magnetic system (which is realistic and has potential for applications) a type of skyrmion interaction that changes the current point of view in the wider soliton community, as it shows the substantial role of a very specific internal skyrmion mode (breathing mode) for the skyrmion interaction and scattering. We therefore believe that it will open a pathway for follow-up works including synergetic ones.
Some references that were very relevant to this work were unfortunately missing in the previous manuscript and they now had to be added. On the other hand, works on skyrmions in synthetic antiferromagnets (SAF) are not cited in the present paper. We think that SAF are not closely enough related to standard AFM especially when dynamics are studied (a common theoretical model cannot be obtained as far as we know). SAF skyrmions are called AFM skyrmions in some works, but we prefer to avoid citations of SAF works, which means that we believe that these two systems (each one very interesting in its own right) can only be studied separately.
We hope that the manuscript, in its present completed form, will be found to meet the criteria for publication in SciPost Physics.
List of changes
In response to the remarks of Report 1
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Section 4 has been added which gives an analytical study that produces an understanding of the interaction behaviour. The skyrmion scale change during the scattering is a central part of the analytics.
In Sec. 3, at the end, a paragraph that was heuristically describing the interaction behaviour has been mostly erased.
In response to the remarks of Report 2
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1. References have been added (but not the ones studying SAF skyrmions, as explained in our response letter).
2. Skyrmion mass is now discussed in Section 4 (e.g., in connection to Fig. 8a).
3. Section 4 now provides a much more precise discussion for skyrmion interaction.
All main changes
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Bruno Barton-Singer was added as co-author.
The abstract was completed to include the analytical results.
Sec. 1. References have been added (now [23], [26], [30]).
Sec. 3. The last paragraph (on heuristic description of skyrmion interaction) has been mostly erased.
Section 4 has been added. It includes Figs. 7,8,9,10 and a number of new References.
Sec. 5 (Conclusions). A phrase has been added at the end of the first paragraph.
Current status:
Reports on this Submission
Strengths
1-Discovery of a novel phenomena (skyrmion interaction process where conversion of kinetic into potential energy leads to shrinking and possible annihilation of skyrmions)
2-Good combination of numerical work with intuitive understanding, based on a simple collective coordinate model
3-Clear structure and exposition
Weaknesses
1-Missing justification of the collective coordinate model (other than that it reproduces the numerics reasonably well
2-Could have explored wider range of scattering processes (eg varying impact parameter)
Report
This is an interesting paper that discusses new phenomena in skyrmion dynamics, using a combination of numerical and approximate analytical methods. The phenomena depend on the combination of `Newtonian' time evolution (second order in d/dt) and the presence of the DMI term in the static energy. The results reported here could have significant impact since the main observation is rather general, and could potentially be applied to many other soliton models. The paper is succinct, well structured and reads well.
Requested changes
1-Clarify the form of `skyrmion' in this model i.e., the precise form of n in (13) and (10)
2-Briefly comment if the breathing of travelling skyrmions leads to oscillations in the linear velocities. The dependence of the mass on the scale R would imply this, but it is not visible in the plots in Figure 9
Recommendation
Publish (meets expectations and criteria for this Journal)