Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Distinguishing $s^{\pm}$ and $s^{++}$ electron pairing symmetries by
  neutron spin resonance in superconducting NaFe$_{0.935}$Co$_{0.045}$As   A determination of the superconducting (SC) electron pairing symmetry forms
the basis for establishing a microscopic mechansim for superconductivity. For
iron pnictide superconductors, the $s^\pm$-pairing symmetry theory predicts the
presence of a sharp neutron spin resonance at an energy below the sum of hole
and electron SC gap energies ($E\leq 2\Delta$) below $T_c$. On the other hand,
the $s^{++}$-pairing symmetry expects a broad spin excitation enhancement at an
energy above $2\Delta$ below $T_c$. Although the resonance has been observed in
iron pnictide superconductors at an energy below $2\Delta$ consistent with the
$s^\pm$-pairing symmetry, the mode has also be interpreted as arising from the
$s^{++}$-pairing symmetry with $E\ge 2\Delta$ due to its broad energy width and
the large uncertainty in determining the SC gaps. Here we use inelastic neutron
scattering to reveal a sharp resonance at E=7 meV in SC
NaFe$_{0.935}$Co$_{0.045}$As ($T_c = 18$ K). On warming towards $T_c$, the mode
energy hardly softens while its energy width increases rapidly. By comparing
with calculated spin-excitations spectra within the $s^{\pm}$ and
$s^{++}$-pairing symmetries, we conclude that the ground-state resonance in
NaFe$_{0.935}$Co$_{0.045}$As is only consistent with the $s^{\pm}$-pairing, and
is inconsistent with the $s^{++}$-pairing symmetry.

13
The categories of this paper are: quant-ph
24
The categories of this paper are: dg-ga
0
The categories of this paper are: hep-ph
26
The categories of this paper are: bayes-an
7
The categories of this paper are: hep-th
35
The categories of this paper are: mtrl-th
33
The categories of this paper are: plasm-ph
14
The categories of this paper are: math-ph
31
The categories of this paper are: ao-sci
32
The categories of this paper are: atom-ph
6
The categories of this paper are: astro-ph
11
The categories of this paper are: hep-lat
2
The categories of this paper are: math
25
The categories of this paper are: patt-sol
22
The categories of this paper are: chao-dyn
1
The categories of this paper are: cs