Momentum matrix elements for angle-resolved UV-photoemission from Cu(111): comparison of experimental data and results from one-step calculations

Abstract

A combined experimental and theoretical analysis of intensities for angle-resolved UV-photoemission out of bulk bands at the Cu(111) surface is presented. We concentrate on the direction and relative magnitude of the momentum matrix elements P fi=〈f| p|i〉 which do not depend on the incident light properties and therefore are very suitable for a comparison of experiment and calculation. Experimental data have been derived from peak intensities measured at fixed electron emission angles θ, but at a large number of light incidence angles ψ i of p-polarized HeI radiation. Theoretical intensities have been extracted from spectra calculated (for the same set of θ, ψ i -combinations) within the fully relativistic formulation of the one-step model. In both cases the determination of P fi relies on the validity of Fresnel's equations, which have been used to calculate the relevant vector potential in the outermost atomic layers of the solid. The results demonstrate that under the experimental conditions of our study the combination of Fresnel's equations and the one-step model gives a qualitatively good description of the observed intensities. Some quantitative discrepancies, however, remain unexplained in this approach.