Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Upper critical fields and thermally-activated transport of
  Nd(O_0.7F_0.3)FeAs single crystal   We present measurements of the resistivity and the upper critical field H_c2
of Nd(O_0.7F_0.3)FeAs single crystals in strong DC and pulsed magnetic fields
up to 45 T and 60 T, respectively. We found that the field scale of H_c2 is
comparable to ~100 T of high T_c cuprates. H_c2(T) parallel to the c-axis
exhibits a pronounced upward curvature similar to what was extracted from
earlier measurements on polycrystalline samples. Thus this behavior is indeed
an intrinsic feature of oxypnictides, rather than manifestation of vortex
lattice melting or granularity. The orientational dependence of H_c2 shows
deviations from the one-band Ginzburg-Landau scaling. The mass anisotropy
decreases as T decreases, from 9.2 at 44K to 5 at 34K. Spin dependent
magnetoresistance and nonlinearities in the Hall coefficient suggest
contribution to the conductivity from electron-electron interactions modified
by disorder reminiscent that of diluted magnetic semiconductors. The Ohmic
resistivity measured below T_c but above the irreversibility field exhibits a
clear Arrhenius thermally activated behavior over 4-5 decades. The activation
energy has very different field dependencies for H||ab and H\perp ab. We
discuss to what extent different pairing scenarios can manifest themselves in
the observed behavior of H_{c2}, using the two-band model of superconductivity.
The results indicate the importance of paramagnetic effects on H_c2(T),which
may significantly reduce H_c2(0) as compared toH_c2(0)~200-300 T based on
extrapolations of H_c2(T) near T_c down to low temperatures.

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The categories of this paper are: nucl-th
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The categories of this paper are: mtrl-th
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The categories of this paper are: quant-ph
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The categories of this paper are: chem-ph
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The categories of this paper are: econ
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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: adap-org
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The categories of this paper are: stat
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The categories of this paper are: gr-qc
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The categories of this paper are: q-fin
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The categories of this paper are: nlin
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The categories of this paper are: atom-ph
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The categories of this paper are: math
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The categories of this paper are: cmp-lg
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The categories of this paper are: acc-phys