Polarized neutron scattering studies of magnetic excitations in iron-selenide superconductor (Li$_{0.8}$Fe$_{0.2}$)ODFeSe ($T_c$ = 41 K)

TL;DR

This study uses polarized neutron scattering to investigate magnetic excitations in the iron-selenide superconductor Li$_{0.8}$Fe$_{0.2}$ODFeSe, revealing an isotropic resonance mode near 21 meV that appears in both superconducting and normal states.

Contribution

First polarized neutron scattering measurements of magnetic excitations in Li$_{0.8}$Fe$_{0.2}$ODFeSe, showing the resonance mode is magnetic and isotropic, highlighting the role of spin-orbit coupling.

Findings

Resonance mode near 21 meV confirmed as magnetic.

Spin excitations are isotropic in the studied energy range.

Resonance mode becomes isotropic when spin-orbit coupling is minimized.

Abstract

We report polarized neutron scattering measurements of the low energy spin fluctuations of the iron-selenide superconductor Li$_{0.8}$Fe$_{0.2}$ODFeSe below and above its superconducting transition temperature $T_c=41$ K. Our experiments confirmed that the resonance mode near 21 meV is magnetic. Moreover, the spin excitations are essentially isotropic in spin space at 5$\leq E\leq$ 29 meV in the superconducting and normal states. Our results suggest that the resonance mode in iron-based superconductors becomes isotropic when the influence of spin-orbit coupling and magnetic/nematic order is minimized, similar to those observed in cuprate superconductors.