Recent developments in the theory of HARPES

Highlights: ► We review theoretical description of HARPES based on the one-step model of photo emission. ► All spin–orbit effects are accounted for by a fully relativistic description. ► The impact of chemical disorder within surface layers can be handled by means of the coherent-potential-approximation. ► Phonon properties allows a direct comparison with features in the HARPES spectra caused by temperature induced disorder. -- Abstract: Various technical developments extended the potential of angle-resolved photo emission spectroscopy tremendously during the last one or two decades. In particular improved momentum and energy resolution as well as the use of photon energies from few eV up to several keV makes this experimental technique a rather unique tool to investigate the electronic properties of solids and surfaces. Obviously, this rises the need for a corresponding theoretical formalism that allows to accompany experimental hard X-ray angle-resolved photo emission (HARPES) studies in an adequate way. This could be achieved by various recent developments on the basis of the one-step model of photo emission: all spin–orbit effects are accounted for by a fully relativistic description. Calculating phonon properties allows a direct comparison with features in the HARPES spectra caused by temperature induced disorder. The same holds for the influence of electronic correlation effects. These are accounted for by means of the dynamical mean field theory that removes the most serious short comings of standard calculations based on the conventional local spin-density approximation. Finally, accounting for the photon momentum and going beyond the single scatterer approximation for the final state allows to deal quantitatively with HARPES