Abstract
We use inelastic neutron scattering to study the temperature dependence of the low-energy spin excitations in single crystals of superconducting FeTe0.6Se0.4 (T-c = 14 K). In the low-temperature superconducting state, the imaginary part of the dynamic susceptibility at the electron and hole Fermi-surfaces nesting wave vector Q = (0.5, 0.5), chi '' (Q, omega), has a small spin gap, a two-dimensional neutron spin resonance above the spin gap, and increases linearly with increasing (h) over bar omega for energies above the resonance. While the intensity of the resonance decreases like an order parameter with increasing temperature and disappears at temperature slightly above T-c, the energy of the mode is weakly temperature dependent and vanishes concurrently above T-c. This suggests that in spite of its similarities with the resonance in electron-doped superconducting BaFe2-x (Co, Ni)(x)As-2, the mode in FeTe0.6Se0.4 is not directly associated with the superconducting electronic gap.
