Exceptional behavior of d-like surface resonances on W(110): the one-step model in its density matrix formulation

Spin-orbit-induced spin splitting of surface states has attracted great interest in recent years because of the high potential for technological applications associated with this phenomenon. This Rashba physics is found in a variety of systems ranging from simple metals like Ag or Au to the so-called topological insulators which are of special interest in spintronics. A very special and unique case is found at the W(110) surface. In this metal d-like surface resonances exhibit energy dispersions and spin-polarization structures which are reminiscent of topological surface states. In our theoretical study, we present a complete analysis of the surface electronic structure of W(110) and show that the atypical linear-shaped dispersion behavior is triggered by the amount of charge transfer from the bulk into the first few vacuum layers. Furthermore, we compare our theoretical spectra with experimental photoemission data on W(110) and demonstrate that our state-of-the-art photoemission theory is able to deal with these peculiar surface features in a quantitative way. Our analysis is based on a generalization of the relativistic one-step model of photoemission, recently extended by us to study photoelectron spectroscopy at high photon energies. This theoretical approach was realized in the full spin-density matrix formulation for the photocurrent, which allows for an unrestricted calculation of the spin-polarization vector of the photoelectron. As an additional result we predict very peculiar behavior of these surface features showing up even at soft and hard x-ray energies. This observation is very surprising, unprecedented for ordinary surface features on simple metal surfaces.