High-resolution angle-resolved photoemission spectra from Ni(100): Matrix element effects and spin-resolved initial and final state bands

We have carried out extensive one- and three-step angle-resolved photoemission spectroscopy (ARPES) intensity computations on Ni(100) within the band theory framework based on the local spin-density approximation. The results show a good overall level of accord with the recent high-resolution ARPES experiments on Ni(100) which probe the majority- and minority-spin ${\Sigma }_1$ band along the $\Gamma -K$ direction near the Fermi energy ${(E}_F),$ uncertainties inherent in our first-principles approach notwithstanding. The ${\mathbf{k}}_{\Vert }$ and energy dependencies of various spectral features are delineated in terms of the interplay between changes in the initial- and final-state bands and the associated transition matrix elements. The remarkable decrease observed with decreasing $k_{\Vert }$ in the ARPES intensity of the majority-spin ${\Sigma }_1$ band as it disperses below the $E_F$ as well as an enhanced spin polarization of the photoemitted electrons from the $E_F$ is shown to arise from the presence of a band gap in the final-state spectrum.