Itinerant approach to magnetic neutron scattering of FeSe: effect of orbital selectivity

Recent STM experiments and theoretical considerations have highlighted the role of interaction-driven orbital selectivity in FeSe, and its role in generating the extremely anisotropic superconducting gap structure in this material.
We study the magnetic excitation spectrum resulting from the coherent quasiparticles within the same renormalized random phase approximation approach used to explain the STM experiments, and show that it agrees well with the low-energy momentum and energy dependent response measured by inelastic neutron scattering experiments. We find a correlation-induced suppression of (π,π) scattering due to a small quasiparticle weight of states of d_xy character [1]. We compare predictions for twinned and untwinned crystals, and predict in particular a strongly (π,0)-dominated susceptibility at low energies in untwinned systems. These results will be discussed in comparison to recent inelastic neutron scattering on detwinned FeSe.
The same description of the coherent quasiparticles is used to make further predictions of physical observables in FeSe such as the magnetic penetration depth which has recently been examined in detail by µSR experiments [2].
[1] A. Kreisel, Brian M. Andersen, P. J. Hirschfeld, arXiv:1807.09482
[2] P. Biswas, et al., arXiv:1810.06269