Electron-doping evolution of the low-energy spin excitations in the iron arsenide superconductor BaFe2−xNixAs2

Abstract

We use elastic and inelastic neutron scattering to systematically investigate the evolution of the low-energy spin excitations of the iron arsenide superconductor BaFe2−xNixAs2 as a function of nickel doping x. In the undoped state, BaFe2As2 exhibits a tetragonal-to-orthorhombic structural phase transition and simultaneously develops a collinear antiferromagnetic (AF) order below TN=143 K. Upon electron doping of x=0.075 to induce bulk superconductivity with Tc=12.2 K, the AF ordering temperature reduces to TN≈58 K. We show that the appearance of bulk superconductivity in BaFe1.925Ni0.075As2 coincides with a dispersive neutron spin resonance in the spin excitation spectra and a reduction in the static ordered moment. For optimally doped BaFe1.9Ni0.1As2 (Tc=20 K) and overdoped BaFe1.85Ni0.15As2 (Tc=14 K) 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.

Source-reported materials — not catalogue approval

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