Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Vacancy ordering and phonon spectrum in the Fe superconductor
  K$_{0.8}$Fe$_{1.6}$Se$_2$   We have performed Raman-scattering measurements on a high-quality single
crystal of the recently discovered Fe-based superconductor
K$_{0.8}$Fe$_{1.6}$Se$_2$ ($T_c$ = 32 K). At least thirteen phonon modes were
observed in the wave number range 10$-$300 cm$^{-1}$. The spectra possess a
four-fold symmetry indicative of bulk vacancy order in the Fe-deficient planes.
We perform a vibration analysis based on first-principles calculations, which
both confirms the ordered structure and allows a complete mode assignment. We
observe an anomaly at $T_c$ in the 180 cm$^{-1}$ $A_g$ mode, which indicates a
rather specific type of electron-phonon coupling.

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The categories of this paper are: hep-ex
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The categories of this paper are: chao-dyn
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The categories of this paper are: patt-sol
34
The categories of this paper are: chem-ph
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The categories of this paper are: hep-lat
1
The categories of this paper are: cs
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The categories of this paper are: dg-ga
3
The categories of this paper are: physics
32
The categories of this paper are: atom-ph
15
The categories of this paper are: nucl-ex
33
The categories of this paper are: plasm-ph
29
The categories of this paper are: funct-an
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The categories of this paper are: q-alg
2
The categories of this paper are: math
26
The categories of this paper are: bayes-an
16
The categories of this paper are: stat