[en] We report an extensive study on the intrinsic bulk electronic structure of the high-temperature superconductor CeFeAsO_0.89F_0.11 and its parent compound CeFeAsO by soft and hard x-ray photoemission, x-ray absorption and soft-x-ray emission spectroscopies. The complementary surface/bulk probing depth, and the elemental and chemical sensitivity of these techniques allows resolving the intrinsic electronic structure of each element and correlating it with the local structure, which has been probed by extended-x-ray absorption fine structure spectroscopy. The measurements indicate a predominant 4f¹ (i.e. Ce³⁺) initial state configuration for Cerium and an effective valence-band-to-4f charge-transfer screening of the core hole. The spectra also reveal the presence of a small Ce f⁰ initial state configuration, which we assign to the occurrence of an intermediate valence state. The data reveal a reasonably good agreement with the partial density of states as obtained in standard density functional calculations over a large energy range. Implications for the electronic structure of these materials are discussed.

[en] Photoelectron emission spectra in a photon energy range between 7.5 and 21 eV are measured for in situ grown polycrystalline Yb films. By comparing bulk and surface core level shifted 4f components we give an estimation of the effective attenuation length (EAL) for low energy (6-20 eV) electrons in Yb, establishing a moderate increase of the EAL upon electron energy decrease. The experimental EAL data are found to be a factor of four smaller than those predicted from the so-called 'universal curve'.

[en] We report systematic temperature- and doping-dependent measurements of the Fe 3s core-level photoemission spectra in the normal state of superconducting Sr(Fe_1-xCo_x)₂As₂. The analysis of the Fe 3s spectrum provides an element-specific determination of the mean value of the magnitude of the Fe spin moment measured on the fast (10^-16-10^-15s) timescale of the photoemission process. The data reveal the ubiquitous presence in the normal state of Fe spin moments with magnitude fluctuating on short timescales. The data reveal a significant reduction of the magnitude of the effective Fe spin moment on going from the parent to the optimal doped compound. The doping dependence of the magnitude of the spin moment at higher doping level is less clear, being either constant, or even nonmonotonic, depending on temperature. This phenomenology indicates the importance of the interaction between spin and itinerant degrees of freedom in shaping the properties of the normal state. These findings reaffirm the complexity of the normal state of 122 Fe-pnictides, which are typically viewed as the least correlated of the high-temperature unconventional superconductors.

[en] At the Elettra synchrotron light laboratory, a new undulator-based beamline with photon energy ranging from about 4.6 to 40 eV has been installed and opened to users. The beamline, based on a 4 m normal-incidence monochromator (NIM) with spherical gratings and movable exit slit, serves an end station to perform primarily high-resolution angle-resolved photoemission spectroscopy experiments in the low photon energy regime. The salient features of the instrument and some of the commission data are reported in this paper.

[en] We report on a combined photoemission and inverse photoemission spectroscopy analysis on Rb_xC₆₀ compounds with different stoichiometries (0-bar x-bar 6). Apart from shifts and broadening of the spectral features associated to the different phase formed, we observe in the RbC₆₀ phase the presence of the highest occupied molecular orbital (HOMO) shoulder and of its symmetric (with respect to the Fermi level) empty state. According to calculations, the metallicity of this phase and the presence of these electronic states may be taken as a fingerprint of the interplay between electron-electron and electron-phonon interactions in determining the electronic behavior of alkali metal fullerides