2019/06/20 by Scherer, Daniel D., Andersen, Brian M.
#FOS: Physical sciences #Strongly Correlated Electrons (cond-mat.str-el) #Superconductivity (cond-mat.supr-con)
paper · doi:10.48550/arxiv.1906.08566
The so-called neutron spin resonance consists of a prominent enhancement of the magnetic response at a particular energy and momentum transfer upon entering the superconducting state of unconventional superconductors. In the case of iron-based superconductors, the neutron resonance has been extensively studied experimentally, and a peculiar spin-space anisotropy has been identified by polarized inelastic neutron scattering experiments. Here we perform a theoretical study of the energy- and spin-resolved magnetic susceptibility in the superconducting state with s+- -wave order parameter, relevant to iron-pnictide and iron-chalcogenide superconductors. Our model is based on a realistic bandstructure including spin-orbit coupling with electronic Hubbard-Hund interactions included at the RPA level. Spin-orbit coupling is taken into account both in the generation of spin-fluctuation mediated pairing, as well as the numerical computation of the spin susceptibility in the superconducting state. We find that spin-orbit coupling and superconductivity in conjunction can reproduce the salient experimentally observed features of the magnetic anisotropy of the neutron resonance. This includes the possibility of a double resonance, the tendency for a c-axis polarized resonance, and the existence of enhanced magnetic anisotropy upon entering the superconducting phase.