Neutron spin resonance as a probe of Fermi surface nesting and superconducting gap symmetry in Ba0.67K0.33(Fe1−xCox)2As2
Maier, Thomas A.
Stone, Matthew B.
We use inelastic neutron scattering to study the energy and wave-vector dependence of the superconductivity-induced resonance in hole-doped Ba0.67K0.33(Fe1−xCox)2As2 (x=0 and 0.08 with Tc≈37 and 28 K, respectively). In previous work on electron-doped Ba(Fe0.963Ni0.037)2As2 (TN=26K and Tc=17 K), the resonance is found to peak sharply at the antiferromagnetic (AF) ordering wave vector QAF along the longitudinal direction, but disperses upwards away from QAF along the transverse direction [Kim et al., Phys. Rev. Lett. 110, 177002 (2013)]. For hole-doped x=0 and 0.08 without AF order, we find that the resonance displays a ringlike upward dispersion away from QAFalong both the longitudinal and transverse directions. By comparing these results with calculations using the random phase approximation, we conclude that the dispersive resonance is a direct signature of isotropic superconducting gaps arising from nested hole-electron Fermi surfaces.