Neutron spin resonance in the new-type iron-based superconductors*

Most iron-based superconductors show a neutron spin resonance which is a typical evidence for the intimate relationship between magnetism and superconductivity. Here we have grown high quality single crystals of the new-type iron-based superconductors CaLa-112 and CaK-1144 [1], and used inelastic neutron scattering to search the spin resonance. Although both system have similar structure to the 122 system, their spin resonance shows very different behaviors. For the CaLa-112 system, spin resonance is a two-dimensional-like mode and no modulations along L direction, consistent with the transport measurements[2]. Polarized neutron scattering indicates the intensity of resonance is spatially isotropic due to the weak spin-orbit coupling or absence of orbital ordering. For the CaK-1144 system, it is surprised to find out three spin resonance modes at different energies, and all of them are high modulated along L direction, suggesting multi-orbital physics or multiple Fermi surface nestings. Therefore, the spin resonance in iron pnictide superconductors is highly system dependent due to orbital physics.

[1] T. Xie et al., Supercond. Sci. Technol. 30, 095002(2017).
[2] D. Sonora et al., Phys. Rev. B 96, 014516 (2017).