Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Spin-Density-Wave Gap with Dirac Nodes and Two-Magnon Raman Scattering
  in BaFe2As2   Raman selection rules for electronic and magnetic excitations in BaFe2As2
were theoretically investigated and applied them to the separate detection of
the nodal and anti-nodal gap excitations at the spin density wave (SDW)
transition and the separate detection of the nearest and the next nearest
neighbor exchange interaction energies. The SDW gap has Dirac nodes, because
many orbitals participate in the electronic states near the Fermi energy. Using
a two-orbital band model the electronic excitations near the Dirac node and the
anti-node are found to have different symmetries. Applying the symmetry
difference to Raman scattering the nodal and anti-nodal electronic excitations
are separately obtained. The low-energy spectra from the anti-nodal region have
critical fluctuation just above TSDW and change into the gap structure by the
first order transition at TSDW, while those from the nodal region gradually
change into the SDW state. The selection rule for two-magnon scattering from
the stripe spin structure was obtained. Applying it to the two-magnon Raman
spectra it is found that the magnetic exchange interaction energies are not
presented by the short-range superexchange model, but the second derivative of
the total energy of the stripe spin structure with respect to the moment
directions. The selection rule and the peak energy are expressed by the
two-magnon scattering process in an insulator, but the large spectral weight
above twice the maximum spin wave energy is difficult to explain by the decayed
spin wave. It may be explained by the electronic scattering of itinerant
carriers with the magnetic self-energy in the localized spin picture or the
particle-hole excitation model in the itinerant spin picture. The magnetic
scattering spectra are compared to the insulating and metallic cuprate
superconductors whose spins are believed to be localized.

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The categories of this paper are: q-bio
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The categories of this paper are: patt-sol
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The categories of this paper are: alg-geom
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The categories of this paper are: hep-lat
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The categories of this paper are: ao-sci
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The categories of this paper are: chao-dyn
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The categories of this paper are: astro-ph
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The categories of this paper are: mtrl-th
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The categories of this paper are: cmp-lg
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The categories of this paper are: bayes-an
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The categories of this paper are: econ
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The categories of this paper are: math
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The categories of this paper are: nlin
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The categories of this paper are: quant-ph
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The categories of this paper are: hep-ph
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The categories of this paper are: q-alg