Incommensurate itinerant antiferromagnetic excitations and spin resonance in the FeTe0.6Se0.4 superconductor

We report on inelastic neutron-scattering measurements that find itinerantlike incommensurate magnetic excitations in the normal state of superconducting ${\text{FeTe}}_{0.6}{\text{Se}}_{0.4}$ $({T}_{c}=14\text{ }\text{K})$ at wave vector ${\mathbf{Q}}_{inc}=(1/2\ifmmode\pm\else\textpm\fi{}ϵ,1/2\ensuremath{\mp}ϵ)$ with $ϵ=0.09(1)$. In the superconducting state only the lower energy part of the spectrum shows significant changes by the formation of a gap and a magnetic resonance that follows the dispersion of the normal-state excitations. We use a four band model to describe the Fermi-surface topology of this iron-based superconductors with the extended $s(\ifmmode\pm\else\textpm\fi{})$ symmetry and find that it qualitatively captures the salient features of these data.