Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Spin-pairing and penetration depth measurements from nuclear magnetic
  resonance in NaFe$_{0.975}$Co$_{0.025}$As   We have performed $^{75}$As nuclear magnetic resonance (NMR) Knight shift
measurements on single crystals of NaFe$_{0.975}$Co$_{0.025}$As to show that
its superconductivity is a spin-paired, singlet state consistent with
predictions of the weak-coupling BCS theory. We use a spectator nucleus,
$^{23}$Na, uncoupled from the superconducting condensate, to determine the
diamagnetic magnetization and to correct for its effect on the $^{75}$As NMR
spectra. The resulting temperature dependence of the spin susceptibility
follows the Yosida function as predicted by BCS for an isotropic, single-valued
energy gap. Additionally, we have analyzed the $^{23}$Na spectra that become
significantly broadened by vortices to obtain the superconducting penetration
depth as a function of temperature with $\lambda_{ab}(0) = 5,327 \pm$
78$\,\AA$.

10
The categories of this paper are: q-bio
25
The categories of this paper are: patt-sol
5
The categories of this paper are: gr-qc
0
The categories of this paper are: hep-ph
32
The categories of this paper are: atom-ph
20
The categories of this paper are: acc-phys
17
The categories of this paper are: q-fin
6
The categories of this paper are: astro-ph
12
The categories of this paper are: nucl-th
1
The categories of this paper are: cs
27
The categories of this paper are: comp-gas
33
The categories of this paper are: plasm-ph
18
The categories of this paper are: econ
8
The categories of this paper are: hep-ex
21
The categories of this paper are: adap-org
35
The categories of this paper are: mtrl-th