Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Internal modes of a skyrmion in the ferromagnetic background in chiral
  magnets   A spin texture called skyrmion has been recently observed in certain chiral
magnets without inversion symmetry. The observed skyrmions are extended objects
with typical linear sizes of 10 nm to 100 nm that contain $10^3$ to $10^5$
spins and can be deformed in response to external perturbations. Weak
deformations are characterized by the internal modes which are localized around
the skyrmion center. Knowledge of internal modes is crucial to assess the
stability and rigidity of these topological textures. Here we compute the
internal modes of a skyrmion in the ferromagnetic background state by numerical
diagonalization of the dynamical matrix. We find several internal modes below
the magnon continuum, such as the mode corresponding to the translational
motion, and different kinds of breathing modes. The number of internal modes is
larger for lower magnetic fields. Indeed, several modes become gapless in the
low field region indicating that the single skyrmion solution becomes unstable,
although a skyrmion lattice is thermodynamically stable. On the other hand, at
high fields only three internal modes exist and the skyrmion is stable even at
higher fields when the ferromagnetic state is thermodynamically stable. We also
show that the presence of out-of-plane easy-axis anisotropy stabilizes the
single skyrmion solution. Finally, we discuss the effects of damping and
possible experimental observations of these internal modes.

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The categories of this paper are: patt-sol
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The categories of this paper are: q-fin
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The categories of this paper are: mtrl-th
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The categories of this paper are: ao-sci
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The categories of this paper are: solv-int
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The categories of this paper are: cmp-lg
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The categories of this paper are: cs
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The categories of this paper are: bayes-an
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The categories of this paper are: quant-ph
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The categories of this paper are: comp-gas
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The categories of this paper are: chao-dyn
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The categories of this paper are: dg-ga
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The categories of this paper are: hep-ph
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The categories of this paper are: nucl-th
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The categories of this paper are: funct-an
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The categories of this paper are: gr-qc