Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Antiferromagnetic ordering in superconducting ${\bf YBa_2Cu_3O_{6.5}}$   Commensurate antiferromagnetic ordering has been observed in the
superconducting high-$Tc$ cuprate ${\rm YBa_{2}Cu_{3}O_{6.5}}$ (${\rm
T_{c}}$=55 K) by polarized and unpolarized elastic neutron scattering. The
magnetic peak intensity exhibits a marked enhancement at $T_{c}$. Zero-field
$\mu $SR experiments demonstrate that the staggered magnetization is not truly
static but fluctuates on a nanosecond time scale. These results point towards
an unusual spin density wave state coexisting with superconductivity.

3
The categories of this paper are: physics
28
The categories of this paper are: alg-geom
36
The categories of this paper are: cmp-lg
22
The categories of this paper are: chao-dyn
16
The categories of this paper are: stat
18
The categories of this paper are: econ
24
The categories of this paper are: dg-ga
1
The categories of this paper are: cs
15
The categories of this paper are: nucl-ex
26
The categories of this paper are: bayes-an
8
The categories of this paper are: hep-ex
11
The categories of this paper are: hep-lat
25
The categories of this paper are: patt-sol
37
The categories of this paper are: supr-con
20
The categories of this paper are: acc-phys
17
The categories of this paper are: q-fin