Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Neutron-scattering measurements of the spin excitations in LaFeAsO and
  Ba(Fe$_{0.953}$Co$_{0.047}$)$_{2}$As$_{2}$: Evidence for a sharp enhancement
  of spin fluctuations by nematic order   Inelastic neutron scattering was employed to investigate the impact of
electronic nematic order on the magnetic spectra of LaFeAsO and
Ba(Fe$_{0.953}$Co$_{0.047}$)$_{2}$As$_{2}$. These materials are ideal to study
the paramagnetic-nematic state, since the nematic order, signaled by the
tetragonal-to-orthorhombic transition at $T_{{\rm S}}$, sets in well above the
stripe antiferromagnetic ordering at $T_{{\rm N}}$. We find that the
temperature-dependent dynamic susceptibility displays an anomaly at $T_{{\rm
S}}$ followed by a sharp enhancement in the spin-spin correlation length,
revealing a strong feedback effect of nematic order on the low-energy magnetic
spectrum. Our findings can be consistently described by a model that attributes
the structural/nematic transition to magnetic fluctuations, and unveils the key
role played by nematic order in promoting the long-range stripe
antiferromagnetic order in iron pnictides.

11
The categories of this paper are: hep-lat
36
The categories of this paper are: cmp-lg
3
The categories of this paper are: physics
13
The categories of this paper are: quant-ph
20
The categories of this paper are: acc-phys
12
The categories of this paper are: nucl-th
29
The categories of this paper are: funct-an
15
The categories of this paper are: nucl-ex
24
The categories of this paper are: dg-ga
31
The categories of this paper are: ao-sci
30
The categories of this paper are: q-alg
9
The categories of this paper are: nlin
0
The categories of this paper are: hep-ph
23
The categories of this paper are: solv-int
32
The categories of this paper are: atom-ph
27
The categories of this paper are: comp-gas