Polarized neutron scattering studies of magnetic excitations in iron-selenide superconductor Li0.8Fe0.2ODFeSe (T c = 41 K)

We report polarized neutron scattering measurements of the low energy spin fluctuations of the iron-selenide superconductor Li0.8Fe0.2ODFeSe 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 ⩽ E ⩽ 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.