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A set of electron-correlation energies as large as 10 eV have been measured for a magnetic 2ML Fefilm deposited on Ag(001). By exploiting the spin selectivity in angle-resolved Auger-photoelectroncoincidence spectroscopy and the Cini-Sawatzky theory, the core-valence-valence Auger spectrumof a spin-polarized system have been resolved: correlation energies have been determined for eachindividual combination of the two holes created in the four sub-bands involved in the decay: majorityand minority spin, as well asegandt2g. The energy difference between final states with paralleland antiparallel spin of the two emitted electrons is ascribed to the spin-flip energy for the final ionstate, thus disentangling the contributions of Coulomb and exchange interactions., Comment: 5 pages, 2 figures, 1 table

The space-charge effect, due to the instantaneous emission of many electrons after the absorption of a single photons pulse, causes distortion in the photoelectron energy spectrum. Two calculation methods have been applied to simulate the expansion during a free flight of clouds of mono- and bi-energetic electrons generated by a high energy pulse of light and their results have been compared. The accuracy of a widely used tool, such as SIMION(R), in predicting the energy distortion caused by the space-charge has been tested and the reliability of its results is verified. Finally we used SIMION(R) to take into account the space-charge effects in the simulation of simple photoemission experiments with a time-of-flight analyzer.

The longstanding problem of interpretation of satellite structures in core level photoemission spectra of metallic systems with a low density of conduction electrons is addressed using the specific example of Sb-doped SnO$_2$. Comparison of {\it ab initio} many-body calculations with experimental hard X-ray photoemission spectra of the Sn 4$d$ states shows that strong satellites are produced by coupling of the Sn core hole to the plasma oscillations of the free electrons introduced by doping. Within the same theoretical framework, spectral changes of the valence band spectra are also related to dynamical screening effects. These results demonstrate that, for the interpretation of electron correlation features in the core level photoelectron spectra of such narrow-band materials, going beyond the homogeneous electron gas electron-plasmon coupling model is essential., Comment: 6 PAGES, 4 FIGURES

We report on our investigation of the electronic structure of Ti$_2$O$_3$ using (hard) x-ray photoelectron and soft x-ray absorption spectroscopy. From the distinct satellite structures in the spectra we have been able to establish unambiguously that the Ti-Ti $c$-axis dimer in the corundum crystal structure is electronically present and forms an $a_{1g}a_{1g}$ molecular singlet in the low temperature insulating phase. Upon heating we observed a considerable spectral weight transfer to lower energies with orbital reconstruction. The insulator-metal transition may be viewed as a transition from a solid of isolated Ti-Ti molecules into a solid of electronically partially broken dimers where the Ti ions acquire additional hopping in the $a$-$b$ plane via the $e_g^{\pi}$ channel, the opening of which requires the consideration of the multiplet structure of the on-site Coulomb interaction., Comment: 7 pages, 4 figures

A direct and element-specific measurement of the local Fe spin moment has been provided by analyzing the Fe 3s core level photoemission spectra in the parent and optimally doped CeFeAsO1-xFx (x = 0, 0.11) and Sr(Fe1 xCox)2As2 (x = 0, 0.10) pnictides. The rapid time scales of the photoemission process allowed the detection of large local spin moments fluctuating on a 10-15 s time scale in the paramagnetic, anti-ferromagnetic and superconducting phases, indicative of the occurrence of ubiquitous strong Hund's magnetic correlations. The magnitude of the spin moment is found to vary significantly among different families, 1.3 \muB in CeFeAsO and 2.1 \muB in SrFe2As2. Surprisingly, the spin moment is found to decrease considerably in the optimally doped samples, 0.9 \muB in CeFeAsO0.89F0.11 and 1.3 \muB in Sr(Fe0.9Co0.1)2As2. The strong variation of the spin moment against doping and material type indicates that the spin moments and the motion of itinerant electrons are influenced reciprocally in a self-consistent fashion, reflecting the strong competition between the antiferromagnetic super-exchange interaction among the spin moments and the kinetic energy gain of the itinerant electrons in the presence of a strong Hund's coupling. By describing the evolution of the magnetic correlations concomitant with the appearance of superconductivity, these results constitute a fundamental step toward attaining a correct description of the microscopic mechanisms shaping the electronic properties in the pnictides, including magnetism and high temperature superconductivity.

We present a core-level photoemission study of Sr3(Ru 1-xMnx)2O7, in which we monitor the evolution of the Ru-3d fine structure versus Mn substitution and probing depth. In both Ru 3d3/2 and 3d5/2 core levels we observe a clear suppression of the metallic features, i.e. the screened peaks, implying a sharp transition from itinerant to localized character already at low Mn concentrations. The comparison between soft and hard x-ray photoemission, which provides tunable depth sensitivity, reveals that the degree of localized/metallic character for Ru is different at the surface than in the bulk., Comment: 10 pages, 4 figures, 1 table

We report an extensive study on the intrinsic bulk electronic structure of the high-temperature superconductor CeFeAsO0.89F0.11 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., Comment: Accepted for publication in Phys. Rev. B

We present a comprehensive study of the photon energy dependence of the valence band photoemission yield in the prototype Mott-Hubbard oxide V2O3. The analysis of our experimental results, covering an extended photon energy range (20-6000 eV) and combined with GW calculations, allow us to identify the nature of the orbitals contributing to the total spectral weight at different binding energies, and in particular to locate the V 4s at about 8 eV binding energy. From this comparative analysis we can conclude that the intensity of the quasiparticle photoemission peak, observed close to the Fermi level in the paramagnetic metallic phase upon increasing photon energy, does not have a significant correlation with the intensity variation of the O 2p and V 3d yield, thus confirming that bulk sensitivity is an essential requirement for the detection of this coherent low energy excitation.

We present an x-ray spectromicroscopic investigation of single-crystalline magnetic FeMn/Co bilayers on Cu(001), using X-ray magnetic circular (XMCD) and linear (XMLD) dichroism at the Co and Fe L3 absorption edges in combination with photoelectron emission microscopy (PEEM). Using the magnetic coupling between the ferromagnetic Co layer and the antiferromagnetic FeMn layer we are able to produce magnetic domains with two different crystallographic orientations of the magnetic easy axis within the same sample at the same time. We find a huge difference in the XMLD contrast between the two types of magnetic domains, which we discuss in terms of intrinsic magneto-crystalline anisotropy of XMLD of the Co layer. We also demonstrate that due to the high sensitivity of the method, the small number of induced ferromagnetic Fe moments at the FeMn-Co interface is sufficient to obtain magnetic contrast from XMLD in a metallic system.