Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Raman scattering study of electron-doped Pr$_x$Ca$_{1-x}$Fe$_2$As$_2$
  superconductors   Temperature-dependent polarized Raman spectra of electron-doped
superconducting Pr$_x$Ca$_{1-x}$Fe$_2$As$_2$ ($x \approx 0.12$) single crystals
are reported. All four allowed by symmetry even-parity phonons are identified.
Phonon mode of B$_{1g}$ symmetry at 222 cm$^{-1}$, which is associated with the
c-axis motion of Fe ions, is found to exhibit an anomalous frequency hardening
at low temperatures, that signals non-vanishing electron-phonon coupling in the
superconducting state and implies that the superconducting gap magnitude
$2\Delta_c < 27$meV.

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The categories of this paper are: atom-ph
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The categories of this paper are: chao-dyn
13
The categories of this paper are: quant-ph
11
The categories of this paper are: hep-lat
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The categories of this paper are: dg-ga
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The categories of this paper are: eess
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The categories of this paper are: funct-an
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The categories of this paper are: supr-con
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The categories of this paper are: nucl-ex
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The categories of this paper are: plasm-ph
3
The categories of this paper are: physics
2
The categories of this paper are: math
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The categories of this paper are: adap-org
6
The categories of this paper are: astro-ph
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The categories of this paper are: cmp-lg
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The categories of this paper are: q-fin