Spin resonance in the superconducting state of Li1-xFexODFe1-ySe observed by neutron spectroscopy

We have performed inelastic neutron-scattering measurements on a powder sample of the superconductor lithium iron selenide hydroxide Li1-xFexODFe1-ySe (x similar or equal to 0.16, y similar or equal to 0.02, T-c = 41 K). The spectrum shows an enhanced intensity below Tc over an energy range of 0.64 x 2 Delta < E < 2 Delta, where Delta is the superconducting gap, and has maxima at the wave vectors Q(1) similar or equal to 1.46 and Q(2) similar or equal to 1.97 angstrom(-1). The behavior of this feature is consistent with the spin-resonance mode found in other unconventional superconductors, and in particular strongly resembles the spin resonance observed in the spectrum of another molecular-intercalated iron selenide Li-0.6(ND2)(0.2)(ND3)(0.8)Fe2Se2. The signal can be described with a characteristic two-dimensional wave-vector (pi, 0.67 pi) in the Brillouin zone of the iron square lattice, consistent with the nesting vector between electron Fermi sheets.