%0 Journal Article
%A Müller, Mathias Christian Thomas David
%A Friedrich, Christoph
%A Blügel, Stefan
%T Acoustic magnons in the long-wavelength limit: Investigating the Goldstone violation in many-body perturbation theory
%J Physical review / B
%V 94
%N 6
%@ 2469-9950
%C Woodbury, NY
%I Inst.
%M FZJ-2016-04610
%P 064433
%D 2016
%X Collective spin excitations in magnetic materials arise from the correlated motion of electron-hole pairs with opposite spins. The pair propagation is described by the transverse magnetic susceptibility, which we calculate within many-body perturbation theory from first principles employing the full-potential linearized augmented-plane-wave formalism. Ferromagnetic materials exhibit a spontaneously broken global rotation symmetry in spin space leading to the appearance of acoustic magnons (zero gap) in the long-wavelength limit. However, due to approximations used in the numerical scheme, the acoustic magnon dispersion exhibits a small but finite gap at Γ. We analyze this violation of the Goldstone mode and present an approach that implements the magnetic susceptibility using a renormalized Green function instead of the Kohn-Sham one. This much more expensive approach shows substantial improvement of the Goldstone-mode condition. In addition, we discuss a possible correction scheme, which involves an adjustment of the Kohn-Sham exchange splitting, which is motivated by the spin-wave solution of the one-band Hubbard model. The new exchange splittings turn out to be closer to experiment. We present corrected magnon spectra for the elementary ferromagnets Fe, Co, and Ni.
%F PUB:(DE-HGF)16
%9 Journal Article
%U <Go to ISI:>//WOS:000382125200003
%R 10.1103/PhysRevB.94.064433
%U https://juser.fz-juelich.de/record/818076