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Conserved momenta of ferromagnetic solitons through the prism of differential geometry
by Xingjian Di, Oleg Tchernyshyov
|As Contributors:||Xingjian Di · Oleg Tchernyshyov|
|Arxiv Link:||https://arxiv.org/abs/2105.03553v2 (pdf)|
|Date submitted:||2021-07-06 07:18|
|Submitted by:||Di, Xingjian|
|Submitted to:||SciPost Physics|
The relation between symmetries and conservation laws for solitons in a ferromagnet is complicated by the presence of gyroscopic (precessional) forces, whose description in the Lagrangian framework involves a background gauge field. This makes canonical momenta gauge-dependent and requires a careful application of Noether's theorem. We show that Cartan's theory of differential forms is a natural language for this task. We use it to derive conserved momenta of the Belavin--Polyakov skyrmion, whose symmetries include translation, global spin rotation, and dilation.
Author comments upon resubmission
We are resubmitting our manuscript in response to the referee reports.
The reports are overall positive, with both reviewers recommending publication of the manuscript in SciPost Physics. The referees raised some questions and suggested a number of improvements, for which we are grateful. We have expanded the manuscript in accordance with these suggestions. Below we outline the changes in the manuscript. Specific queries of the referees have been addressed in our replies to them.
Referee 1 wrote: "the manuscript should strongly benefit from expanding the discussion on physical consequences and, especially, new pair of conserved momenta." We have added Subsection 4.5 "Low-energy dynamics of a skyrmion," in which we spell out the physical significance of the new pair of conserved momenta---the global azimuthal angle and skyrmion spin. In the presence of perturbations beyond the ideal Heisenberg model, these two quantities evolve in time in a prescribed manner. The application of a uniform magnetic field parallel to the ground-state magnetization induces a steady precession of the global azimuthal angle, whereas the injection of a spin-polarized electric current at the center of the skyrmion leads to an expansion or contraction of the skyrmion area (spin). We have also added a few sentences mentioning these consequences to Section 5 "Conclusion."
We hope that you will find the revised manuscript suitable for publication and look forward to your reply.
With best regards,
Submission & Refereeing History
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Reports on this Submission
Anonymous Report 2 on 2021-7-15 (Invited Report)
The authors have addressed all questions. I believe the present version of the manuscript satisfies the SciPost Physics' criteria.
Anonymous Report 1 on 2021-7-15 (Invited Report)
I like the updated version and recommend it for publication in SciPost Physics.