Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Atomically-flat, chemically-stable, superconducting epitaxial thin film
  of iron-based superconductor, cobalt-doped BaFe$_2$As$_2$   Epitaxial growth of Fe-based superconductors such as Co-doped SrFe$_2$As$_2$
(SrFe$_2$As$_2$:Co) was reported recently, but has still insufficient
properties for device application because they have rough surfaces and are
decomposed by reactions with water vapor in an ambient atmosphere. This letter
reports that epitaxial films of Co-doped BaFe$_2$As$_2$ grown at 700 oC show
the onset superconducting transition tempearture of 20 K. The transition is
sharper than those observed on the SrFe$_2$As$_2$:Co films, which would
originate from their improved crystallinity. These films also have
atomically-flat surfaces with steps-and-terraces structures and exhibit
chemical stability against exposure to water vapor.

7
The categories of this paper are: hep-th
31
The categories of this paper are: ao-sci
37
The categories of this paper are: supr-con
26
The categories of this paper are: bayes-an
25
The categories of this paper are: patt-sol
35
The categories of this paper are: mtrl-th
21
The categories of this paper are: adap-org
27
The categories of this paper are: comp-gas
10
The categories of this paper are: q-bio
13
The categories of this paper are: quant-ph
1
The categories of this paper are: cs
28
The categories of this paper are: alg-geom
33
The categories of this paper are: plasm-ph
12
The categories of this paper are: nucl-th
2
The categories of this paper are: math
11
The categories of this paper are: hep-lat