Calculation of optical properties and self-energy shifts for ferromagnetic Ni, Co and Fe

Abstract

The diagonal and off-diagonal elements of the optical conductivity tensors of ferromagnetic Ni, Co and Fe have been calculated using the direct interband transition model from the self-consistent spin-polarized band structures. At low photon energies (<3 eV), most of the interband transitions making peaks in both the diagonal and off-diagonal elements involve the localized 3d character in the minority-spin bands with the majority-spin bands only contributing structureless backgrounds. At higher photon energies, both the majority- and minority-spin bands construct separate peaks with the minority-spin peak being located at higher energies. The energy differences between the two peaks for Ni, Co and Fe are 0.3 eV, 0.8 eV and 1.5 eV respectively, which agree well with the spin-exchange splittings determined from angle-resolved photoemission measurements. For Ni and Co significant differences have been found in energy positions of the interband peaks between the calculated and experimental spectra. An empirical self-energy correction model has been applied, in which the sizes of the energy shifts of the excited-state quasiparticle states from those of the ground state are proportional to the density of d character in each state and the energy difference between each state and the Fermi level. The self-energy-corrected spectra for Ni and Co have been brought into good agreement with the experimental spectra.