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

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$\le E\le$ 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.

10 pages, 4 figures