Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Electron-phonon interaction in the normal and superconducting states of
  MgB2   For the 40K-superconductor MgB2 we have calculated the electronic and
phononic structures and the electron-phonon interaction throughout the
Brillouin zone ab initio. In contrast to the isoelectronic graphite, MgB2 has
holes in the bonding sigma-bands, which contribute 42 per cent to the density
of states: N(0) =0.355 states/(MgB2 eV spin). The total interaction strength,
lambda =0.87 and lambda,tr=0.60, is dominated by the coupling of the
sigma-holes to the bond-stretching optical phonons with wavenumbers in a narrow
range around 590 cm^{-1}. Like the holes, these phonons are quasi
two-dimensional and have wave-vectors close to Gamma-A, where their symmetry is
E. The pi-electrons contribute merely 0.25 to lambda and to lambda,tr. With
Eliashberg theory we evaluate the normal-state resistivity, the density of
states in the superconductor, and the B-isotope effect on Tc and Delta0, and
find excellent agreement with experiments, when available. Tc=40 K is
reproduced with mu*=0.10 and 2Delta0/kB Tc=3.9. MgB2 thus seems to be an
intermediate-coupling e-ph pairing s-wave superconductor.

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The categories of this paper are: q-fin
35
The categories of this paper are: mtrl-th
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The categories of this paper are: eess
0
The categories of this paper are: hep-ph
12
The categories of this paper are: nucl-th
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The categories of this paper are: q-bio
7
The categories of this paper are: hep-th
32
The categories of this paper are: atom-ph
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The categories of this paper are: quant-ph
37
The categories of this paper are: supr-con
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The categories of this paper are: solv-int
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The categories of this paper are: dg-ga
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The categories of this paper are: hep-ex
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The categories of this paper are: adap-org
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The categories of this paper are: nucl-ex
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The categories of this paper are: q-alg