Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Large Thermopower in a Layered Oxide NaCo_2O_4   A transition-metal oxide NaCo_2O_4 is a layered oxide in which CoO_2 and Na
alternately stack along the c axis. Recently we have found that this compound
shows unusually large thermopower with low resistivity, which is comparable to
those of Bi_2Te_3. The negative transverse magnetoresistance and the strongly
temperature-dependent Hall coefficient suggest that electron correlation
dominates the conduction mechanism in NaCo_2O_4.

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The categories of this paper are: astro-ph
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The categories of this paper are: acc-phys
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The categories of this paper are: dg-ga
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The categories of this paper are: hep-lat
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The categories of this paper are: patt-sol
33
The categories of this paper are: plasm-ph
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The categories of this paper are: comp-gas
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The categories of this paper are: hep-ph
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The categories of this paper are: math
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The categories of this paper are: cs
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The categories of this paper are: q-bio
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The categories of this paper are: math-ph
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The categories of this paper are: hep-th
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The categories of this paper are: stat
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The categories of this paper are: alg-geom
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The categories of this paper are: atom-ph