Abstract
We use elastic and inelastic neutron scattering to systematically investigate the evolution of the low-energy spin excitations of the iron arsenide superconductor as a function of nickel doping . In the undoped state, exhibits a tetragonal-to-orthorhombic structural phase transition and simultaneously develops a collinear antiferromagnetic (AF) order below . Upon electron doping of to induce bulk superconductivity with , the AF ordering temperature reduces to . We show that the appearance of bulk superconductivity in coincides with a dispersive neutron spin resonance in the spin excitation spectra and a reduction in the static ordered moment. For optimally doped and overdoped superconductors, the static AF long-range order is completely suppressed and the spin excitation spectra are dominated by a resonance and spin gap at lower energies. We determine the electron-doping dependence of the neutron spin resonance and spin gap energies and demonstrate that the three-dimensional nature of the resonance survives into the overdoped regime. If spin excitations are important for superconductivity, these results would suggest that the three-dimensional characters of the electronic superconducting gaps are prevalent throughout the phase diagram and may be critical for superconductivity in these materials.
5 More- Received 14 February 2010
DOI:https://doi.org/10.1103/PhysRevB.81.174524
©2010 American Physical Society