Large downward renormalization of spin excitation energies in BaKFeAs due to electron correlation effects

Murai, Naoki  ; Kajimoto, Ryoichi  ; Suzuki, Katsuhiro*; Ideta, Shinichiro*; Nakajima, Masamichi*; Ikeda, Hiroaki*; Tanaka, Kiyohisa*

Using inelastic neutron scattering (INS) and angle-resolved photoemission spectroscopy (ARPES), we investigate the spin dynamics of iron-based superconductor BaKFeAs. The INS data show a spin-wave-like dispersive feature, with a zone boundary energy of 200 meV. A random phase approximation (RPA) treatment of the dynamical spin susceptibility, incorporating the band renormalization factor of 3 derived from the ARPES measurements on the same crystals, provides a reasonable description of the observed spin excitations. This analysis shows that the experimental spin excitation peak lies at a much lower energy than the bare value, reflecting a strong renormalization of the quasiparticle band dispersion near the Fermi level due to electron correlation effect. The present results point to a unified framework that connects the magnetic response to the underlying electronic structure of the materials.