Experimental verification of quadrupole-dipole interference in spin-resolved photoionization

Spin-orbit-induced photoelectron spin polarization in angle-resolved photoemission from both atomic and condensed matter targets

The existence of highly spin polarized photoelectrons emitted from non-magnetic solids as well as from unpolarized atoms and molecules has been found to be very common in many studies over the past 40 years. This so-called Fano effect is based upon the influence of the spin-orbit interaction in the photoionization or the photoemission process. In a non-angle-resolved photoemission experiment, circularly polarized radiation has to be used to create spin polarized photoelectrons, while in angle-resolved photoemission even unpolarized or linearly polarized radiation is sufficient to get a high spin polarization. In past years the Rashba effect has become very important in the angle-resolved photoemission of solid surfaces, also with an observed high photoelectron spin polarization. It is the purpose of the present topical review to cross-compare the spin polarization experimentally found in angle-resolved photoelectron emission spectroscopy of condensed matter with that of free atoms, to compare it with the Rashba effect and topological insulators to describe the influence and the importance of the spin-orbit interaction and to show and disentangle the matrix element and phase shift effects therein.The relationship between the energy dispersion of these phase shifts and the emission delay of photoelectron emission in attosecond-resolved photoemission is also discussed. Furthermore the influence of chiral structures of the photo-effect target on the spin polarization, the interferences of different spin components in coherent superpositions in photoemission and a cross-comparison of spin polarization in photoemission from non-magnetic solids with XMCD on magnetic materials are presented; these are all based upon the influence of the spin-orbit interaction in angle-resolved photoemission.

Nondipole effects in photo-double-ionization of He by a vuv photon

We present a dynamical model-independent, ab initio parametrization of the quadrupole transition amplitude for photo-double-ionization of He. An asymmetry of the triple differential cross section induced by the nondipole corrections is discussed and shown to be significant even for an excess energy as low as 80 eV. We provide predictions for two different kinds of experiments in which nondipole effects should be observable with current experimental capabilities.