Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Spin singlet pairing in the superconducting state of NaxCoO2\cdot1.3H2O:
  evidence from a ^{59}Co Knight shift in a single crystal   We report a ^{59}Co Knight shift measurement in a single crystal of the
cobalt oxide superconductor Na_{x}CoO_2\cdot1.3H_2O (T_c=4.25 K). We find that
the shift due to the spin susceptibility, K^s, is substantially large and
anisotropic, with the spin shift along the a-axis K^s_a being two times that
along the c-axis K^s_c. The shift decreases with decreasing temperature (T)
down to T\sim100 K, then becomes a constant until superconductivity sets in.
Both K^s_a and K^s_c decrease below T_c. Our results indicate unambiguously
that the electron pairing in the superconducting state is in the spin singlet
form.

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The categories of this paper are: physics
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The categories of this paper are: q-bio
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The categories of this paper are: cmp-lg
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The categories of this paper are: stat
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The categories of this paper are: bayes-an
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The categories of this paper are: eess
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The categories of this paper are: gr-qc
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The categories of this paper are: nucl-ex
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The categories of this paper are: ao-sci
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The categories of this paper are: quant-ph
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The categories of this paper are: supr-con
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The categories of this paper are: solv-int
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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: atom-ph
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The categories of this paper are: alg-geom