Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Multi-Gap Superconductivity in MgB2: Magneto-Raman Spectroscopy   Electronic Raman scattering studies on MgB2 single crystals as a function of
excitation and polarization have revealed three distinct superconducting
features: a clean gap below 37 cm-1 and two coherence peaks at 109 cm-1 and 78
cm-1 which we identify as the superconducting gaps in \pi- and \sigma-bands and
as the Leggett's collective mode arising from the fluctuation in the relative
phase between two superconducting condensates residing on corresponding bands.
The temperature and field dependencies of the superconducting features have
been established. A phononic Raman scattering study of the E2g boron stretching
mode anharmonicity and of superconductivity induced self-energy effects is
presented. We show that anharmonic two phonon decay is mainly responsible for
the unusually large linewidth of the E2g mode. We observe ~2.5% hardening of
the E2g phonon frequency upon cooling into the superconducting state and
estimate the electron-phonon coupling strength associated with this
renormalization.

17
The categories of this paper are: q-fin
25
The categories of this paper are: patt-sol
35
The categories of this paper are: mtrl-th
14
The categories of this paper are: math-ph
22
The categories of this paper are: chao-dyn
3
The categories of this paper are: physics
24
The categories of this paper are: dg-ga
1
The categories of this paper are: cs
9
The categories of this paper are: nlin
31
The categories of this paper are: ao-sci
12
The categories of this paper are: nucl-th
8
The categories of this paper are: hep-ex
34
The categories of this paper are: chem-ph
15
The categories of this paper are: nucl-ex
26
The categories of this paper are: bayes-an
2
The categories of this paper are: math