Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Anomaly in YBa2Cu4O8 charge distribution below Tc: a zero-field muSR
  study   Zero-field $\mu$SR measurements in $^{63}$Cu isotope enriched and natural
YBa$_2$Cu$_4$O$_8$ powders are presented. The temperature dependence of the
$\mu^+$ relaxation rate is characterized by a sizeable enhancement below T$_c$.
The comparison of the asymmetry decay in the two samples reveals that the
$\mu^+$ relaxation is driven by nuclear dipole interaction from 300 K down to
4.2 K. It is argued that the increase in the relaxation below T$_c$ originates
from a change in $\mu^+$ site, possibly due to a modification in the charge
distribution within CuO chains.

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The categories of this paper are: quant-ph
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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: dg-ga
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The categories of this paper are: eess
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The categories of this paper are: nucl-th
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The categories of this paper are: hep-ex
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The categories of this paper are: hep-lat
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The categories of this paper are: q-alg
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The categories of this paper are: supr-con
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The categories of this paper are: chem-ph
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The categories of this paper are: patt-sol
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The categories of this paper are: comp-gas
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The categories of this paper are: bayes-an
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The categories of this paper are: plasm-ph
1
The categories of this paper are: cs