Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Short-range cluster spin glass near optimal superconductivity in
  BaFe$_{2-x}$Ni$_{x}$As$_{2}$   High-temperature superconductivity in iron pnictides occurs when electrons
are doped into their antiferromagnetic (AF) parent compounds. In addition to
inducing superconductivity, electron-doping also changes the static
commensurate AF order in the undoped parent compounds into short-range
incommensurate AF order near optimal superconductivity. Here we use neutron
scattering to demonstrate that the incommensurate AF order in
BaFe$_{2-x}$Ni$_{x}$As$_{2}$ is not a spin-density-wave arising from the
itinerant electrons in nested Fermi surfaces, but consistent with a cluster
spin glass in the matrix of the superconducting phase. Therefore, optimal
superconductivity in iron pnictides coexists and competes with a mesoscopically
separated cluster spin glass phase, much different from the homogeneous
coexisting AF and superconducting phases in the underdoped regime.

18
The categories of this paper are: econ
6
The categories of this paper are: astro-ph
7
The categories of this paper are: hep-th
1
The categories of this paper are: cs
31
The categories of this paper are: ao-sci
34
The categories of this paper are: chem-ph
37
The categories of this paper are: supr-con
19
The categories of this paper are: eess
36
The categories of this paper are: cmp-lg
30
The categories of this paper are: q-alg
10
The categories of this paper are: q-bio
0
The categories of this paper are: hep-ph
3
The categories of this paper are: physics
8
The categories of this paper are: hep-ex
22
The categories of this paper are: chao-dyn
15
The categories of this paper are: nucl-ex