The propagation of a novel magnetic excitation in the superconducting state, called a spin resonance, has been observed in iron arsenide superconductors for the first time. How the resonance disperses depends upon the direction probed within the single crystals studied. Propagation of the spin resonance reveals details about the superconducting state and highlights qualitative differences between iron arsenide and cuprate superconducting materials. The magnetic excitation appears in the superconducting state with upwards dispersion in iron arsenide superconductors. By contrast, in cuprate superconductors the dispersion is downwards. The neutron scattering measurements designed to study the spin resonance were performed on a single crystal of a nickel-doped barium–iron–arsenide superconductor [Ba(Fe0.963Ni0.037)2As2] at the Spallation Neutron Source and the High Flux Isotope Reactor, U.S. Department of Energy user facilities. Neutron spin resonance is considered to be a hallmark of unconventional superconductivity, thus a detailed understanding is important to future developments of superconducting materials.
Magnonlike Dispersion of Spin Resonance in Ni-doped BaFe2As2