Spin excitations in hole-overdoped iron-based superconductors

Horigane, Kazumasa*; Kiho, Kunihiro*; Fujita, Kei*; Kajimoto, Ryoichi  ; Ikeuchi, Kazuhiko*; Ji, S.*; Akimitsu, Jun*; Lee, C. H.*

We report a study on the spin fluctuations of the hole-overdoped iron-based superconductors BaKFeAs ( = 0.5 and 1.0; = 36 K and 3.4 K, respectively) over the entire Brillouin zone using inelastic neutron scattering. We find that their spin spectra consist of spin wave and chimney-like dispersions. The chimney-like dispersion can be attributed to the itinerant character of magnetism. The band width of the spin wave-like dispersion is almost constant from the non-doped to optimum-doped region, which is followed by a large reduction in the overdoped region. This suggests that the superconductivity is suppressed by the reduction of magnetic exchange couplings, indicating a strong relationship between magnetism and superconductivity in iron-based superconductors.