Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Superconductivity and its Enhancement under High Pressure in "F-free"
  Single Crystals of CeOBiS$_2$   "F-free" CeOBiS$_2$ single crystals have successfully grown, thoroughly
eliminating a concern about F-contamination by using a high-purity CsCl flux.
The obtained crystals have a plate-like shape with a size of 1.0-3.0 mm in the
well-developed plane. Single crystal X-ray structural analysis clearly revealed
that the CeOBiS$_2$ crystallizes with a space group $P4/nmm$ (with lattice
parameters of $a$ = 4.0189(6) {\AA}, $c$ = 13.573(2) {\AA}). The bond valence
sum estimation and X-ray photoelectron spectroscopy analysis showed that the
chemical state of Ce was in the mixed valence of Ce$^{3+}$ and Ce$^{4+}$. The
single crystals show superconductivity with zero resistivity at $\sim$1.3 K.
This is the first conclusive evidence of superconductivity driven by Ce valence
fluctuation in surely non-doped CeOBiS$_2$. The superconducting transition
temperature was enhanced up to $\sim$3.8 K by applying hydrostatic pressure.

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The categories of this paper are: supr-con
28
The categories of this paper are: alg-geom
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The categories of this paper are: chem-ph
13
The categories of this paper are: quant-ph
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The categories of this paper are: patt-sol
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The categories of this paper are: q-alg
15
The categories of this paper are: nucl-ex
6
The categories of this paper are: astro-ph
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The categories of this paper are: ao-sci
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The categories of this paper are: stat
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The categories of this paper are: mtrl-th
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The categories of this paper are: eess
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The categories of this paper are: chao-dyn
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The categories of this paper are: nucl-th
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The categories of this paper are: comp-gas
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The categories of this paper are: q-fin