We use inelastic neutron scattering to study the low-energy spin excitations of 112-type iron pnictide Ca0.82La0.18Fe0.96Ni0.04As2 with bulk superconductivity below Tc=22 K. A two-dimensional spin resonance mode is found around E= 11 meV, where the resonance energy is almost temperature independent and linearly scales with Tc along with other iron-based superconductors. Polarized neutron analysis reveals the resonance is nearly isotropic in spin space without any L modulations. Due to the unique monoclinic structure with additional zigzag arsenic chains, the As 4p orbitals contribute to a three-dimensional hole pocket around Γ point and an extra electron pocket at X point. Our results suggest that the energy and momentum distribution of spin resonance does not directly response to the kz dependence of fermiology, and the spin resonance intrinsically is a spin-1 mode from singlet-triplet excitations of the Cooper pairs in the case of weak spin-orbital coupling.
@article{arxiv.1803.00779,
title = {Neutron spin resonance in the 112-type iron-based superconductor},
author = {Tao Xie and Dongliang Gong and Haranath Ghosh and Abyay Ghosh and Minoru Soda and Takatsugu Masuda and Shinichi Itoh and Frederic Bourdarot and Louis-Pierre Regnault and Sergey Danilkin and Shiliang Li and Huiqian Luo},
journal= {arXiv preprint arXiv:1803.00779},
year = {2018}
}