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It is observed that the line shapes of core levels in photoelectron spectroscopy of Ti, Th, and Ce and some of their inter metallic compounds and lanthanide oxides are directly related to the degree of localization of screening orbitals.PACS numbers: 79.60.CnIn the last few years it has become recognized that a detailed understanding of the mechanism of core-hole screening is crucial in core-level spectroscopies, and in particular in x-ray photoelectron spectroscopy (XPS). These screening processes are often well described by excitonlike models in which the screening electron is considered to occupy an orbital centered on the core-ionized atom,, 1 " 4 In such cases the line shapes of core-level peaks in XPS depend critically on the coupling of the screening levels to the other, delocalized, occupied levels of the initial state (see, e c go, RefSo 5-7). The model derived from the Schonhammer-Gunnarsson (SG) treatment of this problem is shown schematically in Fig 0 1, left side. The role of an empty screening level, cp i9 KINETIC ENERGY FIG. 1. Left: Illustration of the Schonhammer-Gunnarsson model of screening and its implications for the corelevel line shapes. The values of W s /A + were a = 0.94, b = 0.75, c= 0.56, d= 0.38, and U ac was 1.5 A + (Ref. 6).Right: Ce 3d 5 / 2 , Th 4/ 7 / 2 , and Ti 2p 3 / 2 XPS peaks from Ce, CePd 3 , Th, and Ti. The peak binding energies are ~883, -333, and ~ 454 eV for the Ce, Th, and Ti levels, respectively.

Temperature-induced changes in the electronic structure of Fe(100) have been investigated by spin-and angle-resolved photoemission for temperatures between room temperature and the Curie temperature T c . States nearly stationary in energy (T^r^) have been observed for photon energy hv = 60 eV. However, from a strong increase in minority-spin intensity for hv = 3l and 21 eV, a downwards shift of the AJ band is inferred to occur upon heating towards T c for large k vectors. PACS numbers: 75.50.Bb, 75.10.Lp, 79.60.Cn The electronic structure at finite temperatures of the 3d-transition metals Fe, Co, and Ni is currently a matter of strong theoretical interest. Spinpolarized band theory based on the self-consistent local-density-functional description gives an adequate account of the ferromagnetic ground state (e.g., cohesive energy, nonintegral moments). 1 However, controversial attempts have been made recently to describe transition-metal magnetism at finite temperatures. 2 "" 6 The basic common idea is to try to incorporate into the theory the existence of local magnetic moments even above T c . The ferromagnetic-to-paramagnetic phase transition is then governed by thermal disordering of the moments, requiring much less energy than singleparticle spin flips which would involve energy changes as large as the exchange splitting. The controversy is over the spatial extent of correlation among the magnetic moments, which is connected intimately to the present debate on the existence of spin waves above TQ?The ferromagnetic-to-paramagnetic phase transition of Fe has been studied by spin-unresolved, angle-resolved photoemission. 8 However, only by measuring the electron spin explicitly can exchange-split bands be identified unambiguously and the band dispersions be detected, as will be shown below. Furthermore, the spin dynamics at elevated temperatures, as spin rotations around the spontaneous magnetization direction or flips of local magnetic moments which currently are considered to be the driving force for the phase transition, can be observed only by this method. We have therefore, for the first time, performed a spin-, angle-, and energy-resolved photoemission experiment on temperature-induced changes in the electronic structure of Fe. Because of a predicted wave-vector (k) dependence of the temperature dependence of the exchange splitting, 5,9 we employed monochromatized tunable synchrotron radiation from the German storage ring BESSY, allowing selection of initial states with different k.The experiment is similar to a recent one on Ni(110) 10 using a resonance lamp. Total energy resolution, including the linewidth of light, was 0.4 eV at Ai/ = 60 eV and about 0.3 eV at Ai/ = 31 eV. The angular resolution was about ±3° at hv = 60 eV decreasing to about ±4° at hv = 31 eV, resulting in k resolution of about j-of the Brillouin zone. The sample was cleaned in situ by standard surfaceanalysis techniques and its surface conditions were monitored by low-energy electron diffraction and photoelectron spectroscopy. 11 T...

Clean single-crystal surfaces of samarium hexaboride (SmB6) have been investigated by x-ray photoelectron spectroscopy. The results confirm the existence of a mixed configuration of Sm in this compound. Comparison of the valence-band spectrum with that of LaB6 allows an accurate determination of the Srn 4f contribution, and a direct comparison with theoretical Sm'+ and Sm'+ 4f spectra. The effective Coulomb interaction is found to be 7.0~0.2 eV; the lifetime broadening of the Sm'+ 4f spectrum is as large as 1.0 eV, which is one order of magnitude larger than that of the Srn'+ 4f spectrum. The ratio of Sm'+ to Sm' from the 4f photoemission intensities is 0.4 in good agreement with the value deduced from earlier susceptibility and Mossbauer experiments. The investigation of the Sm 4d core levels provides additional evidence for the mixed valence state. The background contribution to the Sm 4d spectrum is determined accurately by comparison with the "tail" associated with the narrow 8 1s line; after background correction, a quantitative comparison with Sm'+ and Sm'+ 4d spectra is performed; good agreement can be obtained by including a large lifetime broadening (0.8 eV) for the Sm'+ 4d spectrum. Our results are discussed in connection with other data on more complex mixed-configuration systems.