Splitting of Resonance Excitations in Nearly Optimally Doped Ba(Fe0.94Co0.06)2As2: An Inelastic Neutron Scattering Study with Polarization Analysis

Magnetic excitations in Ba(Fe0.94Co0.06)(2)As-2 are studied by polarized inelastic neutron scattering above and below the superconducting transition. In the superconducting state, we find clear evidence for two resonancelike excitations. At a higher energy of about 8 meV, there is an isotropic resonance mode with weak dispersion along the c direction. In addition, we find a lower excitation at 4 meV that appears only in the c-polarized channel and whose intensity strongly varies with the l component of the scattering vector. These resonance excitations behave remarkably similar to the gap modes in the antiferromagnetic phase of the parent compound BaFe2As2. DOI: 10.1103/PhysRevLett.110.137001