Possible multiple modes of neutron spin resonance in Ba_1-xK_xFe₂As₂ and BaFe_2-xNi_xAs₂

Motivated by the triple modes of neutron spin resonance with both odd and even L-symmetries in CaKFe₄As₄[1],we use inelasitc neutron scattering to re-investigate the spin resonance in 122 system of iron-based superconductors. In the optimally hole doped Ba_1-xK_xFe₂As₂, the spin resonance has very weak L-dependence both for intensity and center energy, while the H-dependence show a combination with an incommensurate mode at high energy and a commensurate mode at low energy. In the optimally electron doped BaFe_2-xNi_xAs₂, the spin resonance becomes L-dependent at low energy. A very weak even mode (L=2,4, 6...) probably exist around 14 meV. Therefore, in contrast to the explaination based on weak L-dispersion on single spin resonance mode, we propose an alternative explanation based on the multiply Fermi surface nesting induced multi-modes with different symmetries, which give Q-dependent intensity either for out-of-plane or in-plane spin excitations.

[1] T. Xie et al., Phys. Rev. Lett. 120, 267003 (2018)