Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Unconventional London penetration depth in Ba(Fe0.93Co0.07)2As2 single
  crystals   The London penetration depth, $\lambda(T)$, has been measured in several
single crystals of Ba(Fe$_{0.93}$Co$_{0.07}$)$_2$As$_2$. Thermodynamic,
electromagnetic, and structural characterization measurements confirm that
these crystals are of excellent quality. The observed low temperature variation
of $\lambda(T)$ follows a power-law, $\Delta \lambda (T) \sim T^n$ with $n=2.4
\pm 0.1$, indicating the existence of normal quasiparticles down to at least
$0.02T_c$. This is in contrast to recent penetration depth measurements on
single crystals of NdFeAsO$_{1-x}$F$_x$ and SmFeAsO$_{1-x}$F$_x$, which
indicate an anisotropic but nodeless gap. We propose that a more
three-dimensional character in the electronic structure of
Ba(Fe$_{0.93}$Co$_{0.07}$)$_2$As$_2$ may lead to an anisotropic $s-$wave gap
with point nodes that would explain the observed $\lambda(T)$.

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The categories of this paper are: cmp-lg
15
The categories of this paper are: nucl-ex
13
The categories of this paper are: quant-ph
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The categories of this paper are: ao-sci
18
The categories of this paper are: econ
16
The categories of this paper are: stat
7
The categories of this paper are: hep-th
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The categories of this paper are: patt-sol
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The categories of this paper are: alg-geom
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The categories of this paper are: q-fin
8
The categories of this paper are: hep-ex
5
The categories of this paper are: gr-qc
2
The categories of this paper are: math
9
The categories of this paper are: nlin
6
The categories of this paper are: astro-ph
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The categories of this paper are: supr-con