Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Damping of the de Haas-van Alphen oscillations in the superconducting
  state of MgB_2   The de Haas-van Alphen (dHvA) signal arising from orbits on the $\pi$ Fermi
surface sheet of the two-gap superconductor MgB$_2$ has been observed in the
vortex state below $H_{c2}$. An extra attenuation of the dHvA signal, beyond
those effects described in the conventional Lifshitz-Kosevich expression, is
seen due to the opening of the superconducting gap. Our data show that the
$\pi$ band gap is still present up to $H_{c2}$. The data are compared to
current theories of dHvA oscillations in the superconducting state which allow
us to extract estimates for the evolution of the $\pi$ band gap with magnetic
field. Contrary to results for other materials, we find that the most recent
theories dramatically underestimate the damping in MgB$_2$.

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The categories of this paper are: funct-an
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The categories of this paper are: atom-ph
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The categories of this paper are: acc-phys
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The categories of this paper are: math
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The categories of this paper are: comp-gas
8
The categories of this paper are: hep-ex
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The categories of this paper are: cmp-lg
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The categories of this paper are: hep-lat
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The categories of this paper are: hep-th
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The categories of this paper are: patt-sol
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The categories of this paper are: q-bio
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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: q-fin
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The categories of this paper are: nucl-ex
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The categories of this paper are: bayes-an