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

A combined experimental and theoretical analysis of intensities for angle-r esolved UV-photoemission out of bulk bands at the Cu(111) surface is presen ted. 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 p roperties and therefore are very suitable for a comparison of experiment an d calculation. Experimental data have been derived from peak intensities me asured at fixed electron emission angles theta, but at a large number of li ght incidence angles psi(i) of p-polarized HeI radiation. Theoretical inten sities have been extracted from spectra calculated (for the same set of the ta, psi(i)-combinations) within the fully relativistic formulation of the o ne-step model. In both cases the determination of P-fi relies on the validi ty of Fresnel's equations, which have been used to calculate the relevant v ector potential in the outermost atomic layers of the solid. The results de monstrate that under the experimental conditions of our study the combinati on 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. (C) 1999 Elsevier Science B.V . All rights reserved.