Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Upper critical field, anisotropy, and superconducting properties of
  Ba$_{1-x}$K$_x$Fe$_2$As$_2$ single crystals   The temperature dependent resistivity of Ba$_{1-x}$K$_x$Fe$_2$As$_2$ (x =
0.23, 0.25, 0.28 and 0.4) single crystals and the angle dependent resistivity
of superconducting Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$ single crystals were
measured in magnetic fields up to 9 T. The measurements of temperature
dependent resistivity for samples with different doping levels revealed very
high upper critical fields which increase with the transition temperature
monotonously, and a very low superconducting anisotropy ratio
$\Gamma=H_{c2}^{ab}/H_{c2}^c \approx$ 2. By scaling the resistivity in the
frame of the anisotropic Ginzburg-Landau theory, the angle dependent
resistivity of the Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$ single crystal measured with
different magnetic fields at a certain temperature collapsed onto one curve. As
the only scaling parameter, the anisotropy $\Gamma$ was determined
alternatively for each temperature and was found to be between two and three.

27
The categories of this paper are: comp-gas
26
The categories of this paper are: bayes-an
10
The categories of this paper are: q-bio
0
The categories of this paper are: hep-ph
32
The categories of this paper are: atom-ph
21
The categories of this paper are: adap-org
37
The categories of this paper are: supr-con
13
The categories of this paper are: quant-ph
17
The categories of this paper are: q-fin
14
The categories of this paper are: math-ph
31
The categories of this paper are: ao-sci
3
The categories of this paper are: physics
12
The categories of this paper are: nucl-th
7
The categories of this paper are: hep-th
36
The categories of this paper are: cmp-lg
18
The categories of this paper are: econ