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 FeTe0.6Se0.4 (T-c=14 K) at wave vector Q(inc) = (1/2 +/- epsilon, 1/2 -/+ epsilon) with epsilon = 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(+/-) symmetry and find that it qualitatively captures the salient features of these data.