Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Electron-doping evolution of the low-energy spin excitations in the iron
  arsenide BaFe$_{2-x}$Ni$_{x}$As$_{2}$ superconductors   We use elastic and inelastic neutron scattering to systematically investigate
the evolution of the low-energy spin excitations of the iron arsenide
superconductor BaFe2-xNixAs2 as a function of nickel doping x. In the undoped
state, BaFe2As2 exhibits a tetragonal-to-orthorhombic structural phase
transition and simultaneously develops a collinear antiferromagnetic (AF) order
below TN = 143 K. Upon electron-doping of x = 0.075 to induce bulk
superconductivity with Tc = 12.3 K, the AF ordering temperature reduces to TN =
58 K.We show that the appearance of bulk superconductivity in
BaFe1.925Ni0.075As2 coincides with a dispersive neutron spin resonance in the
spin excitation spectra, and a reduction in the static ordered moment. For
optimally doped BaFe1.9Ni0.1As2 (Tc = 20 K) and overdoped BaFe1.85Ni0.15As2 (Tc
= 15 K) superconductors, the static AF long-range order is completely
suppressed and the spin excitation spectra are dominated by a resonance and
spin-gap at lower energies. We determine the electron-doping dependence of the
neutron spin resonance and spin gap energies, and demonstrate that the
three-dimensional nature of the resonance survives into the overdoped regime.
If spin excitations are important for superconductivity, these results would
suggest that the three-dimensional character of the electronic superconducting
gaps are prevalent throughout the phase diagram, and may be critical for
superconductivity in these materials.

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The categories of this paper are: funct-an
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The categories of this paper are: gr-qc
9
The categories of this paper are: nlin
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The categories of this paper are: alg-geom
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The categories of this paper are: nucl-th
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The categories of this paper are: chao-dyn
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The categories of this paper are: econ
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The categories of this paper are: supr-con
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The categories of this paper are: physics
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The categories of this paper are: dg-ga
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The categories of this paper are: bayes-an
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The categories of this paper are: chem-ph
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The categories of this paper are: hep-th
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The categories of this paper are: math-ph
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The categories of this paper are: patt-sol
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The categories of this paper are: cs