The 3D topological insulator material Bi2Se3 is characterized with angle-resolved photoemission spectroscopy (ARPES) energy-momentum intensity spectra at various temperatures. High quality samples with relatively small band gaps and a low energy Dirac point were used. An ideal resolution was deter- mined to be taken at photon energy of 11eV. Scattering interaction at the surface can come from three main sources: electron-phonon, surface impurity, or electron-electron scattering, between the surface and the bulk conduction bands. Momemtum- and Energy- Distribution Curves (MDC and EDC) fits were modeled with Gaussian convoluted Lorentzian and extremely-correlated Fermi liquid theory, respectively. By comparing the binding energy at different temperatures for regions near the Fermi edge and near the Dirac point, and observing an increase in MDC self-energy near the Fermi edge, we conclude that a source of interaction is through phonon coupling channels. By calculating the coupling constant λ from self-energy at various temperatures, we present a very low value of λ = 0.049 ± 0.007 which supports our conclusion that phonon coupling must be incorporated into the theory to provide accurate fit models. Data was taken at beam line 5-4 at the Stanford Synchrotron Radiation Lightsource in Menlo Park, with samples prepared by Genda Gu’s group at Brookhaven National Laboratory.

Surface-related effects in angle-resolved valence spectra of CeRu_2Si_2 at the Ce 4d->$5f resonance threshold for different cleaved surfaces are presented and compared to angle-integrated valence spectra and to bulk-sensitive Ce 3d-edge valence spectra. Evidence that Ce 4d-edge photoemission spectroscopy on ideal cleaved surfaces is dominated by bulk Ce 4f states is presented.

A dramatic temperature dependent enhancement of U 5f spectral weight at EF is observed in angle-resolved photoemission measurements of URu_2Si_2 at the center of an X-point hole-pocket. Comparison of this temperature dependent behavior for excitation both at and below the U 5d->5f resonant threshold is presented.

With the current interest in the rare-earth tellurides as high temperature charge density wave materials, a greater understanding of the physics of these systems is needed, particularly in the case of the ditellurides. We report a detailed study of the band structure of LaTe_2 in the charge density wave state using high-resolution angle resolved photoemission spectroscopy (ARPES). From thiswork we hope to provide insights into the successes and weaknesses of past theoretical study as well as helping to clear up prior ambiguities by providing an experimental basis for future work inthe tellurides.

Boron K-edge soft x-ray emission and absorption are used to address the fundamental question of whether divalent hexaborides are intrinsic semimetals or defect-doped bandgap insulators. These bulk sensitive measurements, complementary and consistent with surface-sensitive angle-resolved photoemission experiments, confirm the existence of a bulk band gap and the location of the chemical potential at the bottom of the conduction band.

Angle-resolved photoemission measurements of divalent hexaborides reveals a >1 eV X-point gap between the valence and conduction bands, in contradiction to the band overlap assumed in several models of their novel ferromagnetism. While the global ARPES band structure and gap size observed are consistent with the results of bulk-sensitive soft x-ray absorption and emission boron K-edge spectroscopy, the surface-sensitive photoemission measurements also show a variation with cation, surface and time of the position of the surface chemical potential in the band structure.