Neutron scattering study of spin dynamics in superconducting (Tl, Rb)2Fe4Se5

We observed in superconducting (Tl, Rb)(2)Fe4Se5 spin-wave branches that span an energy range from 6.5 to 209 meV. Spin dynamics are successfully described by a Heisenberg localized spin model whose dominant in-plane interactions include only the nearest (J(1) and J(1)') and next nearest neighbor (J(2) and J(2)') exchange terms within and between the tetramer spin blocks, respectively. These experimentally determined exchange constants would crucially constrain the theoretical viewpoints on magnetism and superconductivity in the Fe-based materials. DOI: 10.1103/PhysRevB.87.100501