Theoretical limitations to the determination of bandwidth and electron mass renormalization: the case of ferromagnetic iron

Recent experimental advances have allowed electronic band structures to be investigated by angle-resolved photoemission in considerably more detail.A recent study of ferromagnetic iron finds the occupied bandwidth, for the two shallow bands observed, reduced by ∼30% as compared to the calculated ground state, rendering bcc iron comparable with the strongly correlated transition metal Ni.Fermi velocities were reported to deviate from the ground state and these deviations have been assigned entirely to electron correlation.We show that spin-orbit splitting, final-state transitions and finalstate broadening significantly change the band dispersion as measured by a modern energy analyzer, and a simple model that accounts for their effects is introduced.Applying our model, we find for the occupied bandwidth a narrowing of the order of only 10% in agreement with the literature.Substantial renormalization of the Fermi velocities is confirmed but a significantly smaller fraction of it is attributed to correlation effects, namely many-electron interactions.