Angle-resolved Photoemission Spectroscopy Intensity Research Articles

Multiple scattering approach to photoemission from the highest occupied molecular orbital of pentacene

Angle resolved photoemission spectroscopy (ARPES) gives detailed information about the surface electronic structures and oriented molecules. In the so-called orbital tomography method, the ARPES intensity is obtained by a simple Fourier transform of the initial state molecular orbital. While this method has given good results for a number of π-orbital systems, it is known to have strong limitations because the final state is approximated as a plane wave and thus photoelectron scattering is completely neglected. Here we propose an ARPES theory where the initial states are taken from a quantum chemistry method and the final states are calculated in multiple scattering theory. The initial molecular orbitals are reexpanded in a multi-site spherical wave basis and the multiple scattering potential is constructed from the ab initio charge density. These computations are performed algebraically using newly developed algorithms. The method is applied to pentance and the results are compared with the plane wave approximation.

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 ${\ensuremath{\Sigma}}_{1}$ band along the $\ensuremath{\Gamma}\ensuremath{-}K$ direction near the Fermi energy ${(E}_{F}),$ uncertainties inherent in our first-principles approach notwithstanding. The ${\mathbf{k}}_{\ensuremath{\Vert}}$ 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 ${k}_{\ensuremath{\Vert}}$ in the ARPES intensity of the majority-spin ${\ensuremath{\Sigma}}_{1}$ 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.