Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Observation of pseudogap in MgB2   Pseudogap phase in superconductors continues to be an outstanding puzzle that
differentiates unconventional superconductors from the conventional ones
(BCS-superconductors). Employing high resolution photoemission spectroscopy on
a highly dense conventional superconductor, MgB2, we discover an interesting
scenario. While the spectral evolution close to the Fermi energy is
commensurate to BCS descriptions as expected, the spectra in the wider energy
range reveal emergence of a pseudogap much above the superconducting transition
temperature indicating apparent departure from the BCS scenario. The energy
scale of the pseudogap is comparable to the energy of E2g phonon mode
responsible for superconductivity in MgB2 and the pseudogap can be attributed
to the effect of electron-phonon coupling on the electronic structure. These
results reveal a scenario of the emergence of the superconducting gap within an
electron-phonon coupling induced pseudogap.

29
The categories of this paper are: funct-an
36
The categories of this paper are: cmp-lg
22
The categories of this paper are: chao-dyn
10
The categories of this paper are: q-bio
0
The categories of this paper are: hep-ph
9
The categories of this paper are: nlin
8
The categories of this paper are: hep-ex
35
The categories of this paper are: mtrl-th
28
The categories of this paper are: alg-geom
30
The categories of this paper are: q-alg
14
The categories of this paper are: math-ph
13
The categories of this paper are: quant-ph
20
The categories of this paper are: acc-phys
5
The categories of this paper are: gr-qc
16
The categories of this paper are: stat
24
The categories of this paper are: dg-ga