Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Experimental manifestations of the Nb^{4+}-O^{-} polaronic excitons in
  KTa_{0.988}Nb_{0.012}O_{3}   The formation of the photo-polaronic excitons in ABO_{3} perovskite type
oxides has been detected experimentally by means of the photoinduced electron
paramagnetic resonance studies of KTa_{0.998}Nb_{0.012}O_{3} crystals. The
corresponding microwave X-band spectrum at T < 10 K consists of a narrow,
nearly isotropic signal located at g ~ 2 and a strongly anisotropic component.
The first signal, which has a rich structure due to hyperfine interactions with
the lattice nuclei, is attributed to the single trapped charge carriers: the
electrons and/or the holes. The anisotropic spectrum is caused by the axial
centers oriented along the C_{4} pseudo-cubic principal crystalline axes. The
spectrum angular dependence can be described well by an axial center with S =
1, g_{\parallel) = 0.82, g_{\perp} = 0.52 and D = 0.44 cm^{-1}. The anisotropic
spectrum is attributed to the Nb^{4+}-O^{-} polaronic excitons. The temperature
dependence of the anisotropic component is characterized by two activation
energies: the internal dynamics activation E_{a1} = 3.7\pm0.5 meV, which makes
the EPR spectrum unobservable above 10 K, and the destruction energy E_{a2} =
52\pm4 meV. By comparing the anisotropic photo-EPR spectrum and the
photoinduced optical absorption temperature dependencies, we found that the
Nb^{4+}-O^{-} polaronic excitons also manifested themselves via the ~0.7 eV
wide absorption band arising under UV light excitation in the weakly
concentrated KTaO_{3}:Nb crystals.

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The categories of this paper are: chao-dyn
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The categories of this paper are: math
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The categories of this paper are: hep-th
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The categories of this paper are: supr-con
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The categories of this paper are: plasm-ph
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The categories of this paper are: stat
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The categories of this paper are: math-ph
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The categories of this paper are: nlin
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The categories of this paper are: dg-ga
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The categories of this paper are: atom-ph
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The categories of this paper are: q-fin
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The categories of this paper are: econ
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The categories of this paper are: solv-int
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The categories of this paper are: bayes-an
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The categories of this paper are: comp-gas
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The categories of this paper are: eess