Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Electron-Phonon or Hole Superconductivity in $MgB_2$?   The BCS electron-phonon mechanism and the unconventional 'hole mechanism'
have been proposed as explanations for the high temperature superconductivity
observed in $MgB_2$. It is proposed that a critical test of which theory is
correct is the dependence of $T_c$ on hole doping: the hole mechanism predicts
that $T_c$ will drop rapidly to zero as holes are added, while the
electron-phonon mechanism appears to predict increasing $T_c$ for a substantial
range of hole doping. Furthermore, the hole mechanism and electron-phonon
mechanism differ qualitatively in their predictions of the effect on $T_c$ of
change in the $B-B$ distances. We discuss predictions of the hole mechanism for
a variety of observables as a function of doping, emphasizing the expected
differences and similarities with the electron-phonon explanation. The hole
mechanism predicts coherence length and penetration depth to increase and
decrease monotonically with hole doping respectively.

35
The categories of this paper are: mtrl-th
31
The categories of this paper are: ao-sci
36
The categories of this paper are: cmp-lg
30
The categories of this paper are: q-alg
1
The categories of this paper are: cs
2
The categories of this paper are: math
18
The categories of this paper are: econ
20
The categories of this paper are: acc-phys
28
The categories of this paper are: alg-geom
33
The categories of this paper are: plasm-ph
32
The categories of this paper are: atom-ph
3
The categories of this paper are: physics
26
The categories of this paper are: bayes-an
34
The categories of this paper are: chem-ph
13
The categories of this paper are: quant-ph
19
The categories of this paper are: eess