Mapping energy bands in layer compounds from the angular dependence of ultraviolet photoemission

Photoelectron energy spectra have been measured on the layer compounds 1T?TaSe₂ and 1T?TaS₂ at various polar angles of emission. The azimuthal angle was set to select only those photoelectrons propagating in a plane containing the ГMLA points of the Brillouin zone. The results are used to map energy-vs-wave-vector curves which are found to compare favorably with the first principles calculations of Mattheiss.     

Polarization and angular dependencies in the photoemission from gold

An elementary calculation of the polarization and angular dependencies of photoemission from the valence band of gold is presented. The results are applied to experiments using synchrotron radiation as a light source. We show that use of a cylindrical energy analyzer could result in modulations of the relative peak heights in the d-bands. Simple experimental tests of our conclusions are suggested.     

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.     

Origin and doping dependence of the photoemission pseudogap in Cu oxides

A recent report on ARPES on insulating , compared to previous data from and Dy-doped , sheds new light on the origin of the anisotropic pseudogap observed in the normal state of underdoped cuprate oxides. The energy dispersion of the insulator is attributed to strong AF correlations enhanced by the diagonal hopping between magnetic sites, which is progressively deformed by the possibility of nearest neighbour hopping, that increases with hole doping. Received 9 April 1999     

Influence of the symmetry on the circular dichroism in angular resolved core-level photoemission

The model for angular resolved photoemission from adsorbed atoms is extended to account for the non-axial symmetry of atoms in a crystal field. In particular, circular dichroism in the angular distribution (CDAD) is theoretically investigated. A special emphasis is put on the case when incident photons are propagating along the principal axis of an atom in C_nv symmetry. The model, although mainly developed for adsorbates, may also be used as a base for emission from solid surfaces. An extension to simple bulk symmetries, like D_6h for hexagonal or O_h for cubic crystals, is included. The CDAD for normal incidence does not vanish in the extended model and reflects the symmetry of the adsorption site. Scattering induced final state effects are discussed for alkali metal adsorption. A numerical calculation of the emission from the shallow 4p core level of Rb atoms adsorbed in a (√3×√3)−R30° structure on a Pt(111) surface is presented. In this case even the extended photoemission model predicts the absence of CDAD. The appearance of CDAD is only possible due to the scattering of photoelectrons from the neighbouring atoms of the solid.     

Angular dependence and vectorial effect of the photoemission from EuO

An extremely strong dependence of the photoemission on incident angle and polarization of the exciting light is observed for EuO. At an incident angle of 45° the vector ratio reaches values as high as 50. A strong spectral dependence is detected. The effects can be explained by a simple model which is based on the volume photoeffect.     

Experimental band structure of GaSe obtained by angular resolved photoemission

A very detailed experimental band structure of the layered compound GaSe has been obtained in all the symmetry directions of the Brillouin zone for photon energy varying between 21 and 45 eV. It is shown that in this energy range the dispersion curves E (K//) are independent of the final state and that it is also possible, assuming a free electron like conduction band, to have information along the normal to the layers.     

Measurement of the angular characteristics of transition radiation in near and far zones

A method is developed for measuring the angular distribution of radiation in the near zone that excludes the contribution of the sizes of a radiation source to angular characteristics. Using this method, absolute measurements of the angular distribution of coherent transition radiation are performed in the millimeter wavelength range. It is shown that the measured characteristics correspond to the respective theoretical characteristics obtained in the far zone approximation.     

Polarization dependence of angle-resolved photoemission spectroscopy of graphite

We have used variable polarization synchrotron radiation to map the valence band electronic structure of graphite by angle-resolved photoemission spectroscopy (ARPES). The experimental results with two orthogonal linear polarization of light signifies the contribution of either even or odd symmetry with respect to the crystal mirror plane towards the photoemission intensity. The σ₁ and σ₂ valence bands show odd reflection symmetry while the π valence band shows even symmetry with respect to the mirror plane. The measured ARPES spectrum using left and right circular polarized lights shows asymmetry in intensity around M point of the Brillouin zone, which ultimately mimicking different partial wave character of σ₁ and σ₃ bands.     

Temperature and angular momentum dependence of the quadrupole deformation in sd-shell

Temperature and angular momentum dependence of the quadrupole deformation is studied in the middle of the sd-shell for ²⁸Si and ²⁷Si isotopes using the spherical shell model approach. The shell model calculations have been performed using the standard universal sd-shell (USD) interaction and the canonical partition function constructed from the calculated eigensolutions. It is shown that the extracted average quadrupole moments show a transitional behaviour as a function of temperature and the infered transitional temperature is shown to vary with angular momentum. The quadrupole deformation of the individual eigenstate is also analysed.     

Temperature dependence of the Kondo peak in photoemission spectra of YbAgCu4

Temperature dependent photoelectron spectra of the heavy fermion YbAgCu₄ show that the Kondo resonance is strongly depressed with increasing temperature. The observed reduction is fully consistent with the predictions of the Anderson impurity model, and reveals the transition from a Fermi liquid at low temperature to localized moments above the characteristic Kondo temperature. Despite this important experimental confirmation of the model, discrepancies exist between the experimental and calculated linewidth of the resonance. It is argued that a more realistic treatment of the photoemission process would improve the agreement between theory and experiment.     

Selenium and sulfur bonding on Ni(111); angular resolved photoemission

The bonding mechanism of selenium and sulfur on Ni(111) has been investigated by observing the variation of the normal component of the photocurrent as the angle of incidence of the light is varied. The application of simple arguments leads to the assignment of symmetries to the orbitals observed in the photoemission spectra. An interpretation in terms of a Ni₃ cluster model is made and consequences of this model are discussed.     

The angular dependence of X-ray dispersion corrections

The angular dependence of X-ray dispersion corrections is discussed. It is pointed out that angular dependence of the dispersion corrections is not simply a function of the ratio sin/ contrary to numerical data reported in the International Tables for X-ray Crystallography (1983), several books on X-ray diffraction, and other publications.Hönl [1] showed correctly that the dispersion corrections depend on the Bragg angle and X-ray wavelength independently, and this result is supported by experimental investigation of the Borrmann effect using single crystals of silicon and germanium.It is shown how Hönl's method for calculating the angular dependence of dispersion corrections by means of hydrogen-like eigenfunctions can be generalized to more accurate one electron wave functions which are now available in the form of numerical data.     

Surface boundary conditions and angular dependence of the spin-wave resonance spectra

General surface boundary conditions with regard to the surface anisotropy energy E_s(iitv, ø) and changes of the static magnetization tM₀ in the presurface region layer have been formulated. On the example of uniaxial surface anosotropy the influence of these factors on the angular dependence of the SWR spectrum is briefly discussed.     

Anomalous angular dependence of critical current in niobium films

An anomalous angular dependence of the critical current is observed in niobium films. This phenomenon manifests itself in the fact that, under small intensities of the external magnetic field, the critical current attains its maximum in a slightly tilted magnetic field. It is found that the position of the maximum depends on the external magnetic field, as well as on the initial conditions under which the samples were kept. A theoretical model is proposed to explain the results obtained. This model takes into account the effect of diamagnetic properties, pinning of vortices, and the initial conditions on the vortex system in Nb films.