Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Synthesis and Properties of CaFe$_2$As$_2$ Single Crystals   We report the synthesis and basic physical properties of single crystals of
CaFe2As2, an isostructural compound to BaFe2As2 which has been recently doped
to produce superconductivity. CaFe2As2 crystalizes in the ThCr2Si2 structure
with lattice parameters a = 3.907(4) A and c = 11.69(2) A. Magnetic
susceptibility, resistivity, and heat capacity all show a first order phase
transition at T_0 171 K. The magnetic susceptibility is nearly isotropic from 2
K to 350 K. The heat capacity data gives a Sommerfeld coefficient of 8.2 +- 0.3
mJ/molK2, and does not reveal any evidence for the presence of high frequency
(> 300 K) optical phonon modes. The Hall coefficient is negative below the
transition indicating dominant n-type carriers.

12
The categories of this paper are: nucl-th
17
The categories of this paper are: q-fin
13
The categories of this paper are: quant-ph
32
The categories of this paper are: atom-ph
27
The categories of this paper are: comp-gas
6
The categories of this paper are: astro-ph
28
The categories of this paper are: alg-geom
26
The categories of this paper are: bayes-an
22
The categories of this paper are: chao-dyn
34
The categories of this paper are: chem-ph
7
The categories of this paper are: hep-th
18
The categories of this paper are: econ
8
The categories of this paper are: hep-ex
2
The categories of this paper are: math
16
The categories of this paper are: stat
36
The categories of this paper are: cmp-lg