Symmetry characterization of unoccupied states in thick alkaline layers by spin-resolved Auger electron spectroscopy using primary excitation by circularly polarized light

Abstract

Abstract. CVV Auger electrons emitted from K, Rb and Cs layers are studied using spinresolved spectroscopy. Oriented 3p, 4p and 5p hole states are excited by circularly polarized radiation in normal incidence. The photon energies range from 12 to 24 eV. With all h e materials, the degree and sign of the Auger electron spin polarization vary with the photon energy. As an atomic model of the Auger process predicls. and as a comparison of measurement8 with the calculated densities of states shows, the spin polaimtion is essentially determined by the symmetry of the final states reached in the primary (photo)excitation, Just above the excitation threshold, lhe preferential spin direction of the Auger electrons is measured to be panllcl to the spin of the exciting photons corresponding to a predominantly s-lkc symmetsy of the unoccupied final stares reached by the excitation. At higher photon energies the preferential spin direction changes to be antiparallel to the photon spin, corresponding to the mainly d-like symmetry of unoccupied States reached by the excitation.

Relativistic theoretical description for spin-resolvedCVVAuger electron spectroscopy with application to Pd and Fe

“…Using circularly polarized radiation instead would lead to a preferential occupation of the various sublevels of the M 4 and M 5 shells that differ with respect to the magnetic quantum number . As could be demonstrated by Stoppmanns et al 5 for various alkali metals, this leads to a spin-polarized Auger-electron current even for paramagnetic solids. A corresponding theoretical description of this type of experiment has been given by Yuan et al 12 However, these authors accounted in their calculations only for the spin-orbit coupling with respect to the involved core levels.…”

“…3,4 The experiments of these authors were performed by using unpolarized electrons for the excitation step. Using circularly polarized radiation instead leads to spin-polarized CVV Auger electrons even for paramagnetic solids as shown by Stoppmanns et al, for example, for K. 5 Here the spin polarization of the Auger electrons has to be ascribed to a preferential depopulation of the core levels in the M 2,3 shell during the excitation step that differ in their magnetic quantum number . Recently, linearly and circularly polarized radiation has been used also for spin-resolved CVV AES investigations on magnetically ordered systems.…”

Band symmetries of GaSe(0001) studied by spin-resolved electron spectroscopy using circularly polarized radiation

“…The significant preference of I ϩ at the lowenergy edge of the peaks D, E, and F clearly confirms the primary excitation into p-derived states if the Auger decay of the 3d 5/2 core holes is supposed to be a process with the spin polarization transferred to outgoing electrons by the involved valence-band electrons coupled to a singlet. 16 In Fig. 6 the calculated relativistic band structure and the measured results are compared for the unoccupied part.…”

“…In these studies the symmetry of unoccupied states with energies below the vacuum level was determined. [15][16][17] In this paper we extend the studies of the layered semiconductors to GaSe, a material which shows similarities with InSe but very different band symmetries just above the vacuum level. As with InSe the electronic structure of the semiconducting III-VI compound GaSe is interesting from a fundamental point of view: GaSe also crystallizes in a layered structure with strong covalent bonding within the layer, but only weak van der Waals bonding between adjacent layers and shows quasi-two-dimensional properties.…”

“…With an Auger decay of the excited hole states the core hole orientation is transferred to the outgoing Auger electrons. [12][13][14][15][16][17] Therefore, the Auger-electron spin polarization ͑measured as a function of the photon energy͒ is suitable for probing the symmetry of the unoccupied final states being reached by the primary photoexcitation. This is of special interest for unoccupied states below the vacuum level, e.g., with energies between the conduction band minimum and the vacuum level in the case of semiconductors.…”