Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Self-energy Effect of Superconducting Energy Gap in Point-Contact
  Spectra of MgB$_2$   In strong-coupling superconductors with a short electron mean free path the
self-energy effects in the superconducting order parameter play a major role in
the phonon manifestation of the point-contact spectra at the above-gap
energies. We derive asymptotic expressions of the phonon structure in
MgB$%_{2}$ in the case $eV\gg\Delta $ for tunnel, ballistic, and diffusive
point-contacts and show that these expressions not only qualitatively, but also
semi-quantitatively correspond to the measurements of the phonon structure in
the point-contact spectra for the $\pi$-band of MgB$_{2}$ c-axis oriented thin
films.

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The categories of this paper are: astro-ph
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The categories of this paper are: gr-qc
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The categories of this paper are: q-bio
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The categories of this paper are: nucl-ex
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The categories of this paper are: math-ph
20
The categories of this paper are: acc-phys
29
The categories of this paper are: funct-an
3
The categories of this paper are: physics
30
The categories of this paper are: q-alg
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The categories of this paper are: hep-ex
37
The categories of this paper are: supr-con
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The categories of this paper are: quant-ph
25
The categories of this paper are: patt-sol
28
The categories of this paper are: alg-geom
31
The categories of this paper are: ao-sci
2
The categories of this paper are: math