Fig. 1. Inelastic neutron scattering study of superconducting Ba(Fe0.926Co0.074)2As2 reveals anisotropic and quasi-two-dimensional magnetic fluctuations as well as novel quasi-propagating excitations at higher energies.
Inelastic neutron scattering studies of the superconducting iron arsenide compound Ba(Fe0.926Co0.074)2As2 were performed on the ARCS spectrometer at the Spallation Neutron Source which show that magnetic fluctuations exist up to very high energies and display unusual spatial anisotropy in the 2D Fe square layers. At low energies, the anisotropy suggests underlying magnetic frustration in the form of nematic correlations in the J1-J2 model with J1/J2 ∼ 1. The spin resonance observed in the superconducting state displays the same anisotropy. At higher energies (> 100 meV), the anisotropy evolves into split modes, which bears a striking deviation from the ring-like features expected of a typical conical spin-wave dispersion. This study highlights unusual magnetic fluctuations that may play a pivotal role in the unconventional superconductivity of the iron arsenides.
Anisotropic and quasipropagating spin excitations in superconducting Ba(Fe0.926Co0.074)2As2