Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Spin gap behavior and charge ordering in \alpha^{\prime}-NaV_2O_5 probed
  by light scattering   We present a detailed analysis of light scattering experiments performed on
the quarter-filled spin ladder compound $\alpha^\prime$-NaV$_{2}$O$_{5}$ for
the temperature range 5 K$\le$T$\le$300 K. This system undergoes a phase
transition into a singlet ground state at T=34 K accompanied by the formation
of a super structure. For T$\leq$34 K several new modes were detected. Three of
these modes are identified as magnetic bound states. Experimental evidence for
charge ordering on the V sites is detected as an anomalous shift and splitting
of a V-O vibration at 422 cm$^{-1}$ for temperatures above 34 K. The smooth and
crossover-like onset of this ordering at T$_{\rm CO}$= 80 K is accompanied by
pretransitional fluctuations both in magnetic and phononic Raman scattering. It
resembles the effect of stripe order on the super structure intensities in
La$_2$NiO$_{4+\delta}$.

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The categories of this paper are: quant-ph
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The categories of this paper are: funct-an
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The categories of this paper are: math-ph
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The categories of this paper are: eess
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The categories of this paper are: plasm-ph
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The categories of this paper are: q-bio
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The categories of this paper are: hep-ex
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The categories of this paper are: supr-con
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The categories of this paper are: mtrl-th
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The categories of this paper are: gr-qc
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The categories of this paper are: patt-sol
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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: nlin
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The categories of this paper are: comp-gas
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The categories of this paper are: ao-sci