Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Observation of Bulk Superconductivity in NaxCoO2.yH2O and NaxCoO2.yD2O
  Powder and Single Crystals   Poly- and single-crystalline Na$_x$CoO$_2$ has been successfully intercalated
with H$_2$O and D$_2$O as confirmed by X-ray diffraction and thermogravimetric
analysis. Resistivity, magnetic susceptibility, and specific heat measurements
show bulk superconductivity with T$_c$ close to 5 K in both cases. The
substitution of deuterium for hydrogen has an effect on T$_c$ of less than 0.2
K. Investigation of the resistivity anisotropy of Na$_x$CoO$_2\cdot$yH$_2$O
single crystals shows: (a) almost zero resistivity below T$_c$, and (b) an
abrupt upturn at $T^* \sim$ 52 K in both the $\it {ab}$ plane and the $\it {c}$
direction. The implications of our results on the possible superconducting
mechanism will be discussed.

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The categories of this paper are: dg-ga
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The categories of this paper are: chem-ph
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The categories of this paper are: stat
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The categories of this paper are: physics
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The categories of this paper are: quant-ph
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The categories of this paper are: acc-phys
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The categories of this paper are: solv-int
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The categories of this paper are: hep-ex
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The categories of this paper are: econ
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The categories of this paper are: funct-an
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The categories of this paper are: q-fin
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The categories of this paper are: astro-ph
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The categories of this paper are: mtrl-th
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The categories of this paper are: hep-lat
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The categories of this paper are: nlin
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The categories of this paper are: eess