Spin polarized photoemission from NiMnSb

Spin polarized photoemission experiments are reported on NiMnSb which has been predicted to be a halfmetallic ferromagnet. The 100% polarization near photothreshold has not been observed. If an energy gap in the minority electron density-of-states should exist, it will be smaller than 0.5 eV.     

Magnetic linear dichroism in the angular dependence of core-level photoemission from (Ga,Mn)As using hard x rays

We report a study of the electronic properties of the ferromagnetic semiconductor (Ga,Mn)As using magnetic linear dichroism in the angular dependence of Mn 2p photoemission under hard x-ray excitation. Bulk plasmon loss satellites demonstrate that the probed Mn ions are incorporated deep within the GaAs lattice, while the observed large dichroism indicates that the spectra originate from ferromagnetic substitutional Mn. Simulations of the spectra using an Anderson impurity model show that the ferromagnetic Mn 3d electrons of substitutional Mn in (Ga,Mn)As are intermediate between localized and delocalized.     

Spin polarized photoemission from molecular beam epitaxy-grown be-doped GaAs

We have made a comparative study of the performance of spin polarized photocathodes based on molecular beam epitaxy (MBE) grown GaAs with Be-doping and on liquid phase epitaxy (LPE) grown GaAs with Zn-doping. The experiments were performed on GaAs (100), (110), and (111) surfaces atT-300 K. The photoelectron spin polarization (P) of the MBE-photocathodes is face dependent reaching 49% for the (111) surface, a value close to P=50% predicted by theory. In contrast for the LPE-photocathodes P is significantly lower (19P36%). Possible causes for the higher polarization of the MBE-photocathodes are investigated. The influence of the Zn- and Be-dopant is elucidated by theoretical model calculations which shows that replacing the Zn-dopant by Be reduces significantly the depolarization at very low temperatures, but not at room temperature. It is therefore concluded that theinterface region between the GaAs substrate and the MBE-GaAs layer grown on top of it strongly influences the performance of the source.On leave from the Istituto di Fisica Universitá di Modena I-41100 Modena Italy.     

Spin polarized photoemission from La-doped EuO in the vacuum ultraviolet

The spin polarization of photoelectrons emitted form La doped EuO was measured as a function of light energy up to hv = 11 eV, together with the quantum yield. The spectrum of spin polarization can be understood in terms of the energy level diagram of bulk EuO.     

Plasmon excitation in core-level photoemission

The surface and bulk plasmon satellites in photoemission from a core level are calculated, treating the photoelectron quantum mechanically and including plasmon dispersion. The long wavelength plasmon excitations are suppressed by interference between intrinsic and extrinsic processes, giving featureless satellites at low electron kinetic energy. Structure develops as the electron kinetic energy increases.     

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.     

Spin polarized photoemission from the Fe 3s core levels

The origin of the core level splitting in the Fe 3s spectra has been investigated by spin resolved photoemission. The two Fe 3s spectral features, separated by 4.4 eV, are found to be characterized by large and opposite spin polarization. This observation proves that the exchange interaction is the main cause of the Fe 3s splitting.     

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).     

Second harmonic generation polarization microscopy with tightly focused linearly and radially polarized beams

Second harmonic generation microscopy was conducted on rat-tail tendons with linearly and radially polarized beams. Transverse and axial field components were generated in the focal region through tight focusing of linearly and radially polarized. It was found that the generated SHG signals could not be qualitatively explained with a scalar approximation to the electric field at the focus. Only by accounting for the interactions of the axial and transverse components of the electric field interacting through the nonlinear susceptibility χ⁽²⁾ tensor could the SHG images be explained. For the case of collagen we find that the SHG signal varies as a function of the analyzer angle with a cos² or sin² dependency for linearly polarized beams. For tightly focused radially polarized beams we find that the output SHG is radially polarized after collimation and is independent of the analyzer angle.     

Electron spin polarization in the photoemission of NEA GaAs1−x P x

Negative electron affinity GaAs_1–x P _x -photocathodes emit spin-polarized electrons if irradiated with circularly polarized light. The spectra of spin polarization of photoelectrons emitted from crystals with different phosphorus contentx resemble each other in shape but shift to shorter wavelengths with increasingx. Polarization values up to 40% are observed for electrons from crystals withx=0 andx=0.38. Cathodes with higher phosphorus contents increasing fromx=0.65 tox=0.87 and tox = 1.0 deliver photoelectrons with decreasing degrees of spin polarization of 17%, 15%, and 9%, respectively, at maximum.