Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Nonreciprocal Directional Dichroism and Toroidalmagnons in Helical
  Magnets   We investigate a dynamical magnetoelectric effect due to a magnetic resonance
in helical spin structures through the coupling between magnetization and
electric polarization via a spin current mechanism. We show that the magnon has
both the dynamical magnetic moment $\Delta M^\omega$ and the electric moment
$\Delta P^\omega$ ($\perp \Delta M^\omega$), i.e., a dynamical toroidal moment,
under external magnetic fields, and thus it is named the {\em toroidalmagnon}.
The toroidalmagnon exists in most conical spin structures owing to the
generality of the spin current mechanism. In the absorption of electromagnetic
waves, the toroidalmagnon excitation process generally induces a nonreciprocal
directional dichroism as a consequence of an interference of the magnetic and
electric responses.

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The categories of this paper are: gr-qc
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The categories of this paper are: quant-ph
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The categories of this paper are: q-bio
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The categories of this paper are: chao-dyn
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The categories of this paper are: mtrl-th
29
The categories of this paper are: funct-an
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The categories of this paper are: cs
12
The categories of this paper are: nucl-th
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The categories of this paper are: alg-geom
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The categories of this paper are: nucl-ex
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The categories of this paper are: supr-con
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The categories of this paper are: nlin
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The categories of this paper are: q-fin
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The categories of this paper are: hep-ex
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The categories of this paper are: solv-int
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The categories of this paper are: adap-org