Abstract
This work combines two powerful self-energy techniques: the well-known GW method and a self-energy recently developed by us that describes renormalization effects caused by the scattering of electrons with magnons and Stoner excitations. This GT self-energy, which is fully k-dependent and contains infinitely many spin-flip ladder diagrams, was shown to have a profound impact on the electronic band structure of Fe, Co, and Ni. In the present work, we refine the method by combining GT with the GW self-energy. The resulting GWT spectral functions exhibit strong lifetime effects and emergent dispersion anomalies. They are in an overall better agreement with experimental spectra than those obtained with GW or GT alone, even showing partial improvements over local-spin-density approximation dynamical mean-field theory. The performed analysis provides a basis for applying the GWT technique to a wider class of magnetic materials.
Highlights
Many-body spin excitations in interacting electron systems are complex quantum mechanical processes that are fundamental for the description of the properties of magnetic materials
There is experimental evidence that the scattering of propagating electrons and holes on collective and single-particle spin excitations in magnetic materials lead to a renormalization of the quasiparticle band dispersion and to the appearance of characteristic band anomalies in the quasiparticle spectra measured by the angleresolved photoemission spectroscopy (ARPES)[2,3,4,5,6], a claim that was very recently corroborated by a common theoretical and experimental study of photoemission in iron[7]
Progress in photoemission spectroscopy made it possible to obtain ARPES spectra in high-energy and momentum resolution, sufficient to resolve anomalies that may appear in the quasiparticle band dispersion as indicators of genuine many-body scattering processes, such as magnon-induced renormalization effects
Summary
Many-body spin excitations in interacting electron systems are complex quantum mechanical processes that are fundamental for the description of the properties of magnetic materials. The GW selfenergy has a rather sizable real part, which, in the present case, shifts the quasiparticle bands away from the energies where the self-energy’s imaginary part is large This detuning effect can lead to fewer lifetime effects in the GWT spectral function. The GWT quasiparticle peak is located between the ones from GT anomaly is a waterfall (kink) structure in the dispersion of a and GW, but its intensity is strongly suppressed This is because, at spin-down band of Fe along Γ–H at a binding energy of ~1.5 eV, the position of the peak, the imaginary part of GWT happens to be caused by electron scattering with virtual Stoner excitations. We have an was recently predicted by us[7,19] and subsequently confirmed example where the lifetime broadening in GWT is not the npj Computational Materials (2021) 178
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