Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Anomalous impurity effects in the iron-based superconductor
  KFe$_2$As$_2$   High-quality K(Fe$_{1-x}$Co$_x$)$_2$As$_2$ single crystals have been grown by
using KAs flux method. Instead of increasing the superconducting transition
temperature $T_{\rm c}$ through electron doping, we find that Co impurities
rapidly suppress $T_{\rm c}$ down to zero at only $x \approx$ 0.04. Such an
effective suppression of $T_{\rm c}$ by impurities is quite different from that
observed in Ba$_{0.5}$K$_{0.5}$Fe$_2$As$_2$ with multiple nodeless
superconducting gaps. Thermal conductivity measurements in zero field show that
the residual linear term $\kappa_0/T$ only change slightly with $3.4\%$ Co
doping, despite the sharp increase of scattering rate. The implications of
these anomalous impurity effects are discussed.

37
The categories of this paper are: supr-con
18
The categories of this paper are: econ
7
The categories of this paper are: hep-th
1
The categories of this paper are: cs
0
The categories of this paper are: hep-ph
14
The categories of this paper are: math-ph
33
The categories of this paper are: plasm-ph
30
The categories of this paper are: q-alg
9
The categories of this paper are: nlin
27
The categories of this paper are: comp-gas
32
The categories of this paper are: atom-ph
22
The categories of this paper are: chao-dyn
28
The categories of this paper are: alg-geom
21
The categories of this paper are: adap-org
6
The categories of this paper are: astro-ph
2
The categories of this paper are: math