Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Fully gapped superconductivity with no sign change in the prototypical
  heavy-fermion CeCu2Si2   In exotic superconductors including high-$T_c$ copper-oxides, the
interactions mediating electron Cooper-pairing are widely considered to have a
magnetic rather than the conventional electron-phonon origin. Interest in such
exotic pairing was initiated by the 1979 discovery of heavy-fermion
superconductivity in CeCu$_2$Si$_2$, which exhibits strong antiferromagnetic
fluctuations. A hallmark of unconventional pairing by anisotropic repulsive
interactions is that the superconducting energy gap changes sign as a function
of the electron momentum, often leading to nodes where the gap goes to zero.
Here, we report low-temperature specific heat, thermal conductivity and
magnetic penetration depth measurements in CeCu$_2$Si$_2$, demonstrating the
absence of gap nodes at any point on the Fermi surface. Moreover,
electron-irradiation experiments reveal that the superconductivity survives
even when the electron mean free path becomes substantially shorter than the
superconducting coherence length. This indicates that superconductivity is
robust against impurities, implying that there is no sign change in the gap
function. These results show that, contrary to long-standing belief, heavy
electrons with extremely strong Coulomb repulsions can condense into a
fully-gapped s-wave superconducting state, which has an on-site attractive
pairing interaction.

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The categories of this paper are: physics
13
The categories of this paper are: quant-ph
35
The categories of this paper are: mtrl-th
33
The categories of this paper are: plasm-ph
26
The categories of this paper are: bayes-an
5
The categories of this paper are: gr-qc
28
The categories of this paper are: alg-geom
27
The categories of this paper are: comp-gas
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The categories of this paper are: hep-th
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The categories of this paper are: acc-phys
34
The categories of this paper are: chem-ph
22
The categories of this paper are: chao-dyn
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The categories of this paper are: hep-lat
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The categories of this paper are: astro-ph
32
The categories of this paper are: atom-ph
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The categories of this paper are: ao-sci