Spin polarization effects in photoemission from substrate-split localized adsorbate levels

The angle-integrated photo-electron current, which is emitted by circularly polarized light from substrate-split sublevels of localized spin-orbit doublet states of Xe adsorbed on a solid surface is predicted to be strongly spin-polarized. Analysis of this spin polarization promises a good resolution of the sublevel splitting in energy as well as information about the physical origin of the splitting and the symmetry of the adsorption site.     

Emission direction dependence of the magnetic linear dichroism in valence band and core level photoemission from Co/Cu(001)

We have investigated the angular dependence of the magnetic linear dichroism occurring in angle-resolved photoemission (MLDAD) from epitaxial Co films on Cu(001) using unpolarised HeI- and MgK_α-radiation. Spectra were taken while rotating the sample about the magnetisation direction for fixed angle between the directions of light incidence and photoelectron collection. We observe a strong dependence of the MLDAD asymmetry on the electron emission direction with respect to the surface normal showing the importance of photoelectron diffraction in MLDAD.     

Spin polarization in directional photoemission from non-magnetic crystals by unpolarized light

A spin-dependent three-step photoemission formalism for non-magnetic crystals is outlined, in which unpolarized Bloch electrons are diffracted at the surface. Assuming no spin dependence of the excitation process in the bulk, appreciable spin polarization features are obtained for W(001) at off-normal emission, in fairly good agreement with the first angle- and energy-resolved measurements of photo-electron spin polarization (using unpolarized light).     

Circular dichroism in core level photoemission from an adsorbed chiral molecule

The results of experimental measurements and theoretical simulations of circular dichroism in the angular dependence (CDAD) of photoemission from atomic core levels of each of the enantiomers of a chiral molecule, alanine, adsorbed on Cu(110) are presented. Measurements in, and out of, substrate mirror planes distinguish CDAD due to the chirality of the sample and the experimental geometry. The effect due to sample chirality is relatively weak, so such measurements may not provide a routine spectral fingerprint of adsorbate chirality.     

Spin polarization in the photoemission from the 5d-core levels of a thallium film

A thick unordered Tl film has been deposited on Pt(111). Photoemission with photon energies between 20 eV and 27 eV reveals two peaks due to emission from the 5d _3/2-and the 5d _5/2-levels of Tl. The measurements are performed with circularly polarized radiation. Spin analysis allows separation of the photoelectron intensityI into its partsI ₊ with spin polarization vector parallel andI _– antiparallel to the photonspin. For thed _3/2-and thed _5/2-level the ratioI ₊/I _– turns out to be approximately 31 and 11.8 respectively. These values are close to the values expected ford-level photoionization of free atoms if spin orbit interaction in the final states is neglected. A slight crystal field splitting of 0.2 eV is observed for thed _5/2-level. The data are compared with results for the photoemission from Pb films [1] and data for the photoionization from thed-levels of Hg [2].     

Surface plasmon satellites in x-ray photoemission from core states of adsorbed atoms

It is shown that the kinetic energy spectrum of electrons emitted from core levels of atoms adsorbed on metal surfaces should exhibit surface plasmon satellites. At sufficiently high energies, the satellites arise only via the so-called “intrinsic” mechanism, namely, screening of a suddenly created hole by the metal electrons. Their observation for a suitable adsorption system would thus constitute the first unequivocal evidence for the “intrinsic” effect.     

Spin and charge polarization around magnetic impurities in metals

Our previously developed trial function scheme has been generalized to investigate the spin and charge polarization around the nearest neighbors of the impurity, and the influence of the polarization on the formation of local moments. While the reduction of impurity moment is mostly due to the charge polarization effect, both spin and charge polarizations together yield a polarized moment which compensates up to 60% of the impurity moment. Special case of cluster with completely compensated moment is also considered.     

EELS analysis of cation valence states and oxygen vacancies in magnetic oxides

Transition metal oxides are a class of materials that are vitally important for developing new materials with functionality and smartness. The unique properties of these materials are related to the presence of elements with mixed valences of transition elements. Electron energy-loss spectroscopy (EELS) in the transmission electron microscope is a powerful technique for measuring the valences of some transition metal elements of practical importance. This paper reports our current progress in applying EELS for quantitative determination of Mn and Co valences in magnetic oxides, including valence state transition, quantification of oxygen vacancies, refinement of crystal structures, and identification of the structure of nanoparticles.     

Spin polarization of two-dimensional electron system in different Laughlin states and around filling factor

The spin configuration of the ground state of a two-dimensional electron system is investigated for different FQHE states from an analysis of circular polarization of time-resolved luminescence. The method clearly distinguishes between fully spin polarized, partially spin polarized and spin unpolarized FQHE ground states. We demonstrate that FQHE states which are spin unpolarized or partially polarized at low magnetic fields become fully spin polarized at high fields. Temperature dependence of the spin polarization reveals a nonmonotonic behavior at . At and the electron system is found to be fully spin polarized. This result does not indicate the existence of any skyrmionic excitations in high magnetic field limit. However, at the observed spin depolarization of electron system at and becomes broader for lower magnetic fields, so that full spin polarization remains only in a small vicinity of . Such a behavior could be considered as a precursor of skirmionic depolarization, which would dominate for smaller ratios between Zeeman and Coulomb energies.We demonstrate that the spin polarization of 2D-electron system at and can be strongly affected by hyperfine interaction between electrons and optically spin-oriented nuclears. This result is due to the fact that hyperfine interaction can both enhance and suppress effective Zeeman splitting in fixed external magnetic field.     

Spin current and polarization in impure two-dimensional electron systems with spin-orbit coupling

We derive the transport equations for two-dimensional electron systems with Rashba spin-orbit interaction and short-range spin-independent disorder. In the limit of slow spatial variations, we obtain coupled diffusion equations for the electron density and spin. Using these equations we calculate electric-field induced spin accumulation and spin current in a finite-size sample for an arbitrary ratio between spin-orbit energy splitting Delta and elastic scattering rate tau(-1). We demonstrate that the spin-Hall conductivity vanishes in an infinite system independent of this ratio.