Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Strong anisotropy of superexchange in the copper-oxygen chains of
  La_{14-x}Ca_{x}Cu_{24}O_{41}   Electron spin resonance data of Cu^{2+} ions in La_{14-x}Ca_{x}Cu_{24}O_{41}
crystals (x=9,11,12) reveal a very large width of the resonance line in the
paramagnetic state. This signals an unusually strong anisotropy of ~10% of the
isotropic Heisenberg superexchange in the Cu-O chains of this compound. The
strong anisotropy can be explained by the specific geometry of two symmetrical
90 degree Cu-O-Cu bonds, which boosts the importance of orbital degrees of
freedom. Our data show the apparent limitations of the applicability of an
isotropic Heisenberg model to the low dimensional cuprates.

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The categories of this paper are: gr-qc
35
The categories of this paper are: mtrl-th
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The categories of this paper are: nucl-th
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The categories of this paper are: quant-ph
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The categories of this paper are: hep-th
1
The categories of this paper are: cs
31
The categories of this paper are: ao-sci
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The categories of this paper are: eess
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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: bayes-an
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The categories of this paper are: adap-org
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The categories of this paper are: math-ph
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The categories of this paper are: chao-dyn
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The categories of this paper are: comp-gas
37
The categories of this paper are: supr-con