Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Studies of superconductivity and structure for CaC6 to pressures above
  15 GPa   The dependence of the superconducting transition temperature Tc of CaC6 has
been determined as a function of hydrostatic pressure in both helium-loaded gas
and diamond-anvil cells to 0.6 and 32 GPa, respectively. Following an initial
increase at the rate +0.39(1) K/GPa, Tc drops abruptly from 15 K to 4 K at 10
GPa. Synchrotron x-ray measurements to 15 GPa point to a structural transition
near 10 GPa from a rhombohedral to a higher symmetry phase.

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The categories of this paper are: eess
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The categories of this paper are: econ
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The categories of this paper are: q-fin
8
The categories of this paper are: hep-ex
29
The categories of this paper are: funct-an
5
The categories of this paper are: gr-qc
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The categories of this paper are: adap-org
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The categories of this paper are: comp-gas
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The categories of this paper are: q-alg
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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: atom-ph
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The categories of this paper are: plasm-ph
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The categories of this paper are: hep-th
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The categories of this paper are: hep-lat
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The categories of this paper are: alg-geom