Determination of the pairing state in iron-based superconductors through neutron scattering

We calculate the spin susceptibility in the $s_{\pm }$ and $s_{++}$ superconducting states of the iron pnictides using the effective five-orbital model and considering the quasiparticle damping. For the experimentally evaluated magnitude of the quasiparticle damping and the superconducting gap, the results at the wave vector $\simeq (\pi ,0)$ show that the $s_{\pm }$ state is more consistent with the neutron scattering experiments, while for larger quasiparticle damping and the superconducting gap, the $s_{++}$ state can be more consistent. To distinguish between two cases that reproduce the experiments at the wave vector $\simeq (\pi ,0)$, we propose to investigate experimentally the wave vector $\simeq (\pi ,\pi )$.

Figure 1

Energy dependence of $\chi {}^{″}(\mathit{Q},E)$ at $\mathit{Q}=(\pi ,\pi /16)$ with the quasiparticle damping of ${\gamma }_0=10$ meV. $s_{\pm }$ (circle), $s_{++}$ (triangle), and normal (square) states. We take (a) ${\Delta }_0=5$ meV and $U=1.375$ eV, and (b) ${\Delta }_0=10$ meV and $U=1.3$ eV.

Figure 2

Energy dependence of $\chi {}^{″}(\mathit{Q},E)$ at $\mathit{Q}=(\pi ,\pi /16)$ in the case of (a) $s_{++}$ and (b) $s_{\pm }$ with ${\Delta }_0=25$ meV, the quasiparticle damping ${\gamma }_0=50$ meV, and $U=1.3$ eV.

Figure 3

Energy dependence of $\chi {}^{″}(\mathit{Q},E)$ at $\mathit{Q}=(\pi ,\pi )$ for parameter values where (a)$s_{\pm }$ and (b)$s_{++}$ states are consistent with the experiments at the wave vector $\simeq (\pi ,0)$. (a) ${\Delta }_0=5$ meV, $U=1.375$ eV, and ${\gamma }_0=10$ meV, and (b) ${\Delta }_0=25$ meV, $U=1.3$ eV, and ${\gamma }_0=50$ meV.