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Unveiling the physics that governs the intertwining between the nanoscale self-organization and the dynamics of insulator-to-metal transitions (IMTs) is key for controlling on demand the ultrafast switching in strongly correlated materials and nanodevices. A paradigmatic case is the IMT in ${\mathrm{V}}_{2}{\mathrm{O}}_{3}$, for which the mechanism that leads to the nucleation and growth of metallic nanodroplets out of the supposedly homogeneous Mott insulating phase is still a mystery. Here, we combine x-ray photoemission electron microscopy and ultrafast nonequilibrium optical spectroscopy to investigate the early-stage dynamics of isolated metallic nanodroplets across the IMT in ${\mathrm{V}}_{2}{\mathrm{O}}_{3}$ thin films. Our experiments show that the low-temperature monoclinic antiferromagnetic insulating phase is characterized by the spontaneous formation of striped polydomains, with different lattice distortions. The insulating domain boundaries accommodate the birth of metallic nanodroplets, whose nonequilibrium expansion can be triggered by the photoinduced change of the $3d$-orbital occupation. We address the relation between the spontaneous nanotexture of the Mott insulating phase in ${\mathrm{V}}_{2}{\mathrm{O}}_{3}$ and the timescale of the metallic seeds growth. We speculate that the photoinduced metallic growth can proceed along a nonthermal pathway in which the monoclinic lattice symmetry of the insulating phase is partially retained.

The interaction between phonons and high-energy excitations of electronic origin in cuprates and their role in the superconducting mechanisms is still controversial. Here we use coherent vibrational time-domain spectroscopy together with density functional and dynamical mean-field theory calculations to establish a direct link between the c-axis phonon modes and the in-plane electronic charge excitations in optimally doped YBCO. The non-equilibrium Raman tensor is measured by means of the broadband 'coherent-phonon' response in pump-probe experiments and is qualitatively described by our model using DFT in frozen phonon approximation plus single band DMFT to account for the electronic correlations. The major outcome of our experimental and theoretical study is to establish the link between out-of-plane copper ions displacements and the in-plane electronic correlations, and to estimate at few unit cells the correlation length of the associated phonon mode. The approach introduced here could help revealing the complex interplay between fluctuations of different nature and spatial correlation in several strongly-correlated materials.

A long-standing question for avant-garde data storage technology concerns the nature of the ultrafast photoinduced phase transformations in the wide class of chalcogenide phase-change materials (PCMs). Overall, a comprehensive understanding of the microstructural evolution and the relevant kinetics mechanisms accompanying the out-of-equilibrium phases is still missing. Here, after overheating a phase-change chalcogenide superlattice by an ultrafast laser pulse, we indirectly track the lattice relaxation by time resolved x-ray absorption spectroscopy (tr-XAS) with a sub-ns time resolution. The approach to the tr-XAS experimental results reported in this work provides an atomistic insight of the mechanism that takes place during the cooling process; meanwhile a first-principles model mimicking the microscopic distortions accounts for a straightforward representation of the observed dynamics. Finally, we envisage that our approach can be applied in future studies addressing the role of dynamical structural strain in PCMs.

The extraordinary electronic and optical properties of the crystal-to-amorphous transition in phase-change materials have led to important developments in memory applications. A promising outlook is offered by nanoscaling such phase-change structures. Following this research line, we study the interband optical transmission spectra of nanoscaled $\text{GeTe}/{\mathrm{Sb}}_{2}{\mathrm{Te}}_{3}$ chalcogenide superlattice films. We determine, for films with varying stacking sequence and growth methods, the density and scattering time of the free carriers, and the characteristics of the valence-to-conduction transition. It is found that the free carrier density decreases with increasing GeTe content, for sublayer thicknesses below $\ensuremath{\sim}3$ nm. A simple band model analysis suggests that GeTe and ${\mathrm{Sb}}_{2}{\mathrm{Te}}_{3}$ layers mix, forming a standard GeSbTe alloy buffer layer. We show that it is possible to control the electronic transport properties of the films by properly choosing the deposition layer thickness, and we derive a model for arbitrary film stacks.

MnSi has been extensively studied for five decades; nonetheless detailed information on the Fermi surface (FS) symmetry is still lacking. This missed information prevents a comprehensive understanding of the nature of the magnetic interaction in this material. Here, by performing angle-resolved photoemission spectroscopy on high-quality MnSi films epitaxially grown on Si(111), we unveil the FS symmetry and the evolution of the electronic structure across the paramagnetic-helimagnetic transition at ${T}_{C}\phantom{\rule{4pt}{0ex}}\ensuremath{\sim}40\phantom{\rule{0.28em}{0ex}}\mathrm{K}$, along with the appearance of sharp quasiparticle emission below ${T}_{C}$. The shape of the resulting FS is found to fulfill robust nesting effects. These effects can be at the origin of strong magnetic fluctuations not accounted for by the state-of-the-art quasiparticle self-consistent $\mathit{GW}$ approximation. From this perspective, the unforeseen quasiparticle damping detected in the paramagnetic phase and relaxing only below ${T}_{C}$, along with the persistence of the $d$-band splitting well above ${T}_{C}$, at odds with a simple Stoner model for itinerant magnetism, opens the search for exotic magnetic interactions favored by FS nesting and affecting the quasiparticle lifetime.

We investigate the evolution of both the occupied and unoccupied electronic structure in representative compounds of the infinitely adaptive superlattice series (Sb2)m−Sb2Te3 (m=0–3) by means of angle-resolved photoemission spectroscopy and time-delayed two-photon photoemission, combined with first-principles band-structure calculations. We discover that the topological nature of the surface states and their spin texture are robust, with dispersions evolving from linear (Dirac-like) to parabolic (Rashba-like) along the series, as the materials evolve from semiconductors to semimetals. Our findings provide a promising strategy for engineering the topological states with the desired flexibility needed for realizing different quantum phenomena and spintronics applications.

Bulk Rashba systems BiTeX (X = I, Br, Cl) are emerging as important candidates for developing spintronics devices because of the coexistence of spin-split bulk and surface states, along with the ambipolar character of the surface charge carriers. The need to study the spin texture of strongly spin-orbit-coupled materials has recently promoted circular dichroic angular resolved photoelectron spectroscopy (CD-ARPES) as an indirect tool to measure the spin and the angular degrees of freedom. Here we report a detailed photon-energy-dependent study of the CD-ARPES spectra in BiTeX (X = I, Br, Cl). Our work reveals a large variation in the magnitude and sign of the dichroism. Interestingly, we find that the dichroic signal modulates differently for the three compounds and for the different spin-split states. These findings show a momentum and photon-energy dependence for the CD-ARPES signals in the bulk Rashba semiconductor BiTeX (X = I, Br, Cl). Finally, the outcome of our experiment indicates the important relation between the modulation of the dichroism and the phase differences between the wave functions involved in the photoemission process. This phase difference can be due to initial- or final-state effects. In the former case the phase difference results in possible interference effects among the photoelectrons emitted from different atomic layers and characterized by entangled spin-orbital polarized bands. In the latter case the phase difference results from the relative phases of the expansion of the final state in different outgoing partial waves.

The x-ray-photoemission spectra of the core levels and valence-band region of ${\mathrm{NiS}}_{2}$ is interpreted in terms of a cluster model in the impurity limit. The d-d and p-d charge-fluctuation parameters are evaluated and the nature of the lowest-lying ionization state is investigated.

X-ray (Al-K\ensuremath{\alpha}) and resonant Cu 2p\ensuremath{\rightarrow}3d and Cu 3p\ensuremath{\rightarrow}3d photoemission valence-band spectra of high-quality ${\mathrm{CuGeO}}_{3}$ single crystals are reported and interpreted. In addition, an attempt is given to evaluate the charge transfer (\ensuremath{\Delta}), the d-d Coulomb interaction (${\mathrm{U}}_{\mathrm{dd}}$ ) energies, and the superexchange term (J) on the basis of ${\mathrm{L}}_{2,3}$ ${\mathrm{M}}_{4,5}$ ${\mathrm{M}}_{4,5}$ -${\mathrm{L}}_{2,3}$ ${\mathrm{M}}_{2,3}$ ${\mathrm{M}}_{4,5}$ Auger transitions, and core-level spectra analyzed within the frame of the Anderson Hamiltonian in the impurity limit. The results clearly show that one-electron band-structure calculations do not account for the band gap \ensuremath{\approx}3.7 eV [M. Bassi, P. Camagni, R. Rolli, G. Samoggia, F. Parmigiani, and A. Revcolevschi (unpublished)] and the emission arising from many-body effects (correlated ${\mathrm{d}}^{8}$ and ${\mathrm{d}}^{8}$ -${\mathrm{d}}^{9}$ L hybridized states), while \ensuremath{\Delta} and ${\mathrm{U}}_{\mathrm{dd}}$ , found to be \ensuremath{\approx}4.2 and \ensuremath{\approx}6.7 eV, respectively, allow us to classify this compound as a charge-transfer insulator with a strong ionic character. In addition, energy-dependent electron-energy-loss measurements suggest that the forbidden d-d intraband transitions are centered at \ensuremath{\approx}1.6 eV, which justifies the blue color of ${\mathrm{CuGeO}}_{3}$ , and the band gap is \ensuremath{\approx}3.7 eV, as required by the transparency of the crystal in the visible region of the electromagnetic spectrum. Finally, in the approximation allowed by the present models, J results to be of the order of -7 meV.

We investigate the electronic structure of the Sr${}_{n+1}$Ru${}_{n}$O${}_{3n+1}$ family $(n=1,2,3)$ in the vicinity the Fermi level by means of polarization-dependent resonant O 1$s$ x-ray emission spectroscopy. Using both energy window and polarization analysis we disentangle the contribution of apical and planar oxygen, and compare it with first-principles calculations. Our results provide a new insight on the nature of the oxygen bonds and the role of Sr $3d$ states.

The nature of the Dirac quasiparticles in topological insulators calls for a direct investigation of the electron-phonon scattering at the surface. By comparing time-resolved ARPES measurements of the topological insulator Bi2Se3 with different probing depths, we show that the relaxation dynamics of the electronic temperature of the conduction band is much slower at the surface than in the bulk. This observation suggests that surface phonons are less effective in cooling the electron gas in the conduction band.

The electronic structure of the Rh-based CuRh${}_{0.9}$Mg${}_{0.1}$O${}_{2}$ oxide thermoelectric compound has been studied with a multitechnique approach consisting of photoemission, x-ray absorption, and x-ray emission spectroscopies. The data indicate that the region of the valence band in the proximity of the Fermi level is dominated by Rh-derived states. These findings outline the importance of the electronic structure of the Rh ions for the large thermoelectric power in CuRh${}_{0.9}$Mg${}_{0.1}$O${}_{2}$ at high temperature.

We have performed angle- and spin-resolved photoemission measurements on Fe${}_{3}$O${}_{4}$(0 0 1)/MgO(0 0 1). Despite intrinsic electron-lattice (polaron) interaction a Fe ${t}_{2g}$ band dispersion is observed, as well as a Fermi surface. The states close to the Fermi level show a spin polarization up to $\ensuremath{-}72$$%$ as measured with a 4.65 eV laser light. All the data can be simulated starting from GGA+U bulk band-structure calculations and taking into account the polaron and initial-state lifetime broadening involved in the photoemission process. This conciliates the electronic structure of Fe${}_{3}$O${}_{4}$ with a band model and confirms the half-metallic nature of Fe${}_{3}$O${}_{4}$.

This paper reports experimental evidence for an incipient epitaxial growth of vanadium oxide at the ${\mathrm{TiO}}_{2}$(110) surface. This finding is based on a x-ray photoelectron diffraction and low-energy electron diffraction study of a submonolayer of vanadium deposited at the ${\mathrm{TiO}}_{2}$(110) surface, performed after annealing at 473 K in ultrahigh vacuum conditions. The data unambiguously show that vanadium atoms occupy selected sixfold-coordinated titanium sites which underbridge oxygen atoms of the topmost layer and that the ${\mathrm{TiO}}_{2}$(110) long-range surface structural order is preserved. \textcopyright{} 1996 The American Physical Society.

The absorption coefficient of CuGe${\mathrm{O}}_{3}$ was measured in the energy range of 1-4 eV, in a temperature interval between 300 and 20 K, for light polarized along the $b$ and $c$ crystal axes. A weak absorption band at 1.7 eV is attributed to copper $d\ensuremath{-}d$ transitions partially allowed by electron-phonon interactions; this is followed by a region of transparency leading to a strong exponential edge above 3 eV, which is identified with the onset of charge-transfer transitions.

This paper presents spectroscopic investigations of the normal-state properties of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} and Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{ital y}} single crystals. Ultraviolet photoemission and electron energy loss data are consistent with the filling in of the charge transfer gap upon doping due to spectral weight transfer mechanisms. The modifications occurring in the surface electronic properties after exposure to pure O{sub 2} and after the deposition of one monolayer of bismuth are studied and discussed.

We exploit time- and angle-resolved photoemission spectroscopy to determine the evolution of the out-of-equilibrium electronic structure of the topological insulator Bi2Se3. The response of the Fermi-Dirac distribution to ultrashort IR laser pulses has been studied by modeling the dynamics of hot electrons after optical excitation. We disentangle a large increase in the effective temperature (T*) from a shift of the chemical potential (mu*), which is consequence of the ultrafast photodoping of the conduction band. The relaxation dynamics of T* and mu* are k independent and these two quantities uniquely define the evolution of the excited charge population. We observe that the energy dependence of the nonequilibrium charge population is solely determined by the analytical form of the effective Fermi-Dirac distribution.

Revealing the nature of charge excitations in strongly correlated electron systems is crucial to understanding their exotic properties. Here we use broadband ultrafast pump-probe spectroscopy in the visible range to study low-energy transitions across the Mott-Hubbard gap in the orbitally ordered insulator YVO${}_{3}$. Separating thermal and nonthermal contributions to the optical transients, we show that the total spectral weight of the two lowest peaks is conserved, demonstrating that both excitations correspond to the same multiplet. The pump-induced transfer of spectral weight between the two peaks reveals that the low-energy one is a Hubbard exciton, i.e., a resonance or a nearly bound state between a doublon and a holon. Finally, we speculate that the pump-driven spin disorder can be used to quantify the kinetic energy gain of the excitons in a ferromagnetic environment.

An experimental and theoretical study of the electronic structure of ${\mathrm{K}}_{2}$${\mathrm{NiF}}_{4}$ is presented. Core-level and valence-band x-ray angle-integrated photoemission experiments are reported and the data analyzed through a configuration-interaction impurity-cluster model. The charge transfer and the Mott-Hubbard charge fluctuations are studied and the energies involved estimated. The effect of these mechanisms on the spectral structures is identified. The comparison of local-density-functional band calculations with angle-resolved photoemission experiments shows significant discrepancies. This demonstrates that electron-correlation effects are indeed important and one-electron band-structure calculations are inadequate to describe this compound.

The electronic structure of a ${\mathrm{Bi}}_{2}$${\mathrm{CuO}}_{4}$ single crystal is investigated by x-ray photoelectron (XPS), x-ray Auger-electron (XAES), and electron-energy-loss (EELS) spectroscopies. The analysis of the XPS and XAES data confirms that ${\mathrm{Bi}}_{2}$${\mathrm{CuO}}_{4}$ is a charge-transfer insulator with a band gap of about 2 eV, while the Cu-O bond in ${\mathrm{Bi}}_{2}$${\mathrm{CuO}}_{4}$ is more ionic than in CuO and the ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}\mathrm{Ca}{\mathrm{Cu}}_{2}{\mathrm{O}}_{8\ensuremath{-}\ensuremath{\delta}}$ superconductor. Furthermore, the density of the empty states is tentatively described from a combined analysis of the EELS and XPS data and some electronic transitions are identified from the EELS spectra.

The identification of electronic states and the analysis of their evolution with $n$ is key to understanding $n$-layered ruthenates. To this end, we combine polarization-dependent O 1$s$ x-ray absorption spectroscopy, high-purity Sr${}_{n+1}$Ru${}_{n}$O${}_{3n+1}$ ($n=1,2,3$) single crystals, and ab initio and many-body calculations. We find that the energy splitting between the empty ${x}^{2}\ensuremath{-}{y}^{2}$ and $3{z}^{2}\ensuremath{-}1$ state is considerably smaller than previously suggested and that, remarkably, Sr bands are essential to understanding the spectra. At low energy, we identify the main difference among the materials with a substantial rearrangement of ${t}_{2g}$ orbital occupations with increasing $n$. This rearrangement is controlled by the interplay of Coulomb repulsion, dimensionality, and changes in the ${t}_{2g}$ crystal field.

Here we report extensive ultrafast time-resolved reflectivity experiments on overdoped Bi${}_{2}$Sr${}_{2}$Ca${}_{1\ensuremath{-}x}$Y${}_{x}$Cu${}_{2}$O${}_{8+\ensuremath{\delta}}$ single crystals ($T$${}_{c}=78$ K) aimed to clarify the nature of the superconducting-to-normal-state photoinduced phase transition. The data show a lack of the quasiparticle decay time divergence at the fluence required to induce this phase transition, in contrast to the thermally driven phase transition observed at $T$${}_{c}$ and at variance with recently reported photoinduced transitions from charge-density and spin-density waves to a metal. Our data demonstrate the nonthermal character of the superconducting-to-normal-state photoinduced phase transition. The data are analyzed using an ad-hoc time-dependent Rothwarf-Taylor model, opening the question of the order of this nonequilibrium phase transition.

We report an extensive study on the intrinsic bulk electronic structure of the high-temperature superconductor ${\text{CeFeAsO}}_{0.89}{\text{F}}_{0.11}$ and its parent compound CeFeAsO by soft and hard x-ray photoemissions, x-ray absorption, and soft x-ray emission spectroscopies. The complementary surface/bulk probing depth, and the elemental and chemical sensitivity of these techniques allow 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 $4{f}^{1}$ (i.e., ${\text{Ce}}^{3+}$) 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 $\text{Ce}\text{ }{f}^{0}$ 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.

We report the experimental evidence of an abrupt transition of the ultrafast electronic response of underdoped superconducting ${\text{Bi}}_{2}{\text{Sr}}_{2}{\text{CaCu}}_{2}{\text{O}}_{8+\ensuremath{\delta}}$, under the impulsive photoinjection of a high density of excitations, using ultrashort laser pulses and avoiding significant laser heating. The direct proof of this process is the discontinuity of the transient optical electronic response, observed at a critical fluence of ${\ensuremath{\Phi}}_{\text{th}}\ensuremath{\simeq}70\text{ }\ensuremath{\mu}\text{J}/{\text{cm}}^{2}$. Below this threshold, the recovery dynamics is described by the Rothwarf-Taylor equations, whereas, above the critical intensity, a fast electronic response is superimposed to a slower dynamics related to the superconductivity recovery. We discuss our experimental findings within the frame of the available models for nonequilibrium superconductivity, i.e., the ${T}_{\text{eff}}$ and ${\ensuremath{\mu}}_{\text{eff}}$ models. The measured critical fluence is compatible with a first-order photoinduced phase transition triggered by the impulsive shift of the chemical potential. The measured value, significantly in excess of the condensation energy, indicates that, close to the threshold, the largest amount of energy is delivered to phonons or to other gap-energy excitations strongly coupled to Cooper pairs.

Site-, elemental-, and orbital-resolved partial density of states in ${\text{KCuF}}_{3}$ single crystal have been obtained by polarization-dependent x-ray absorption and emission spectroscopy measurements across the $\text{F}\text{ }K$-edge and ab initio full-multiple-scattering cluster calculations. The $\text{F}\text{ }K$ x-ray absorption spectroscopy spectra show well-defined polarization dependence. The measurements reveal strong overlap between $\text{Cu}\text{ }3d$ and $\text{F}\text{ }2p$ states and identify clearly the $\text{F}\text{ }2{p}_{z}$ and $\text{F}\text{ }2{p}_{x,y}$ empty states created at different F sites. The calculations, performed for the nonequivalent F sites in the structure, confirm the energy overlap, the charge transfer between $\text{Cu}\text{ }3d$ and $\text{F}\text{ }2p$ states, and the different $\text{F}\text{ }2p\text{-Cu}\text{ }3d$ overlap for the two nonequivalent F sites of ${\text{KCuF}}_{3}$. Across the $\text{F}\text{ }K$ edge, resonant x-ray emission spectroscopy detects a broad peak due to $d\text{\ensuremath{-}}d$ excitations centered at about 1.2--1.6 eV and an intense charge-transfer-like transition around 7 eV.

We have performed angle-resolved-photoemission experiments and local-density-functional (LDA) band calculations on NiO to study correlation and band effects of this conceptually important compound. Our experimental result suggests a dual nature of the electronic structure of NiO. On the one hand, the LDA band calculation has some relevance to the electronic structure of NiO, and the inclusion of the antiferromagnetic order is essential. For the lower O 2p bands, the LDA calculation agrees almost perfectly with experimental energy positions and dispersion relations. On the other hand, discrepancies between the experiment and the LDA calculation do exist, especially for the Ni 3d bands and the O 2p bands that are heavily mixed with the Ni 3d bands. It appears that the main discrepancies between the experimental results and the LDA calculation are concentrated in the regions of the insulating gap and the valence-band satellite. In addition to these results, we also report the interesting angle and photon-energy dependence of the satellite emission. The above results show that the angle-resolved-photoemission studies can provide much additional information about the electronic structure of correlated materials like NiO.

Sintered bulk samples of the orthorhombic, superconducting, phase of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ exhibit a \ensuremath{\simeq}1.5 eV Ba core-level decrease compared to the tetragonal, nonsuperconducting phase. This is also observed for thin-film material in the two phases. Using ab initio cluster calculations, we show that shifts of this magnitude are explainable by isotropic contraction of the Ba-O bond length in the 0.01- to 0.02-\AA{} range, values compatible with the known lattice-parameter changes between the phases. Finally, even in situ cleaved good-quality single crystals of the orthorhombic phase show a chemically shifted Ba component for some regions of the surface, which may be due to Ba-O bond-length contractions at the surface-vacuum interface.

High-quality ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{CaCu}}_{2}$${\mathrm{O}}_{8+\mathrm{\ensuremath{\delta}}}$ superconducting single crystals, annealed at different oxygen partial pressures, have been studied using angular-resolved x-ray photoelectron spectroscopy with a resolution higher than that used in any previous study. Two states of the oxygen, separated by \ensuremath{\approxeq}0.7 eV, are unambiguously observed. Examining these components at different angles makes it possible to distinguish bulk from surface components. Using this capability we discover that annealing under lower oxygen partial pressure (1 atm) results in oxygen intercalation beneath the Bi-O surface layer of the crystal, whereas for higher-pressure anneals (12 atm) additional oxygen is found on the Bi-O surfaces. This steplike intercalation mechanism is also confirmed by the changes observed in the Cu and Bi core lines as a function of the annealing oxygen partial pressure.

We present results of resonant-photoemission and high-resolution x-ray-photoemission-spectroscopy (XPS) studies on single-crystalline CuO, which confirms most of the earlier data obtained from polycrystalline samples. However, some minor differences with earlier results were also observed, which are concentrated on a mainly oxygen-related feature. The important first ionization state is much better resolved in our high-resolution XPS data, and is found to have both copper and oxygen orbital character. This is consistent (though not a proof) with the theoretical prediction that the first ionization state is a {sup 1}{ital A}{sub 1{ital g}} singlet with holes on both oxygen and copper sites. The 16-eV satellite is found to show a Cu antiresonance, and is assigned to a {sup 1}{ital A}{sub 1{ital g}} singlet with both holes on the copper sites.

The absence of a clear signature of the Zhang-Rice singlet in the photoelectron valence band spectra of copper germanate raised the question of the stability of this state, induced by one-electron removal processes, in large-gap systems. Following Okada and Kotani [Phys. Rev. B 63, 045103 (2001)], we have performed a study of the O $1s$ resonant x-ray emission for $\mathrm{Cu}{\mathrm{Ge}}_{1\ensuremath{-}x}{\mathrm{Si}}_{x}{\mathrm{O}}_{3}$ ($x=0$, 0.05, and 0.1) single crystals as a function of temperature and polarization. Our experiment shows that the temperature, angle, and polarization dependence of the inelastic scattering emission detected at a $3.6\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ Raman shift in the O $1s$ resonant x-ray spectra can be unambiguously identified with the Zhang-Rice-singlet excitation.

The charge transfer dynamics of an underdoped manganite is probed by resonant x-ray emission and Auger electron spectroscopies at the $\mathrm{Mn}\phantom{\rule{0.3em}{0ex}}{L}_{3}$ edge. The dispersion of peak positions, as the incident photon energy is tuned through the absorption threshold, gives direct information on the relaxation rate in terms of the core-hole lifetime and the localization behavior of the states involved. The charge transfer time is found to be around $0.45\phantom{\rule{0.3em}{0ex}}\mathrm{fs}$, with a dependency on the final state $d$-band occupancy.

This article reports ab initio Fermi surfaces and conduction-band calculations of both stoichiometric and oxygen-reduced ${\mathrm{MoO}}_{3}.$ The data, based on a TB-LMTO approach in LDA, provide a convincing and detailed interpretation of the one-electron removal XPS valence bands, where a clear energy gap is observed for the stoichiometric samples, whereas a significant emission at the Fermi edge is measured for the oxygen reduced system. In addition, the electrical conductivity, as deduced from the shape of the calculated Fermi surface, is confined in the xz plane of the crystal, as required for Luttinger-liquid behavior. These results, when compared to the conduction mechanism observed in the blue bronze ${\mathrm{K}}_{0.3}{\mathrm{MoO}}_{3},$ clearly suggest that oxygen reduction and doping can bring to very different processes for the electronic transport.

Resonant photoemission spectroscopy data from ${\mathrm{Cd}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{Te}$ single crystals are presented. A strong resonant behavior, related to the Raman-Auger decay channel arising from the creation of the Mn $2p$ core hole, is detected for states in the valence-band region at the Mn $2\stackrel{\ensuremath{\rightarrow}}{p}3d$ absorption threshold. The transition from the resonating Raman-Auger to the weak, normal Auger emission is shown to occur well above the main absorption edge. This effect is ascribed to the presence of a manifold of localized states arising from the Mn $2\stackrel{\ensuremath{\rightarrow}}{p}3d$ Coulomb and exchange interaction, which prevents the delocalization in the intermediate state of the autoionization process.

A sum rule is derived that relates the exchange coupling between core and open valence shell electrons in correlated systems to the main and satellite features of their complex photoemission spectra. The principle focus of our analysis is on the photoionization of the metal $2s$ and $3s$ shells in ionic transition-metal compounds. In spite of charge-transfer and near-degeneracy effects, which may induce a considerable redistribution of the spectral weight among a manifold of configurations, this rule points out that the exchange splitting evaluated with the sum rule is equal to the value obtained with the ground-state exchange integral for the material. Application of the sum rule to ${\mathrm{MnF}}_{2}$ and NiO shows that the exchange integral given by the sum rule is very close to that calculated for the free ion; this shows the dominant ionic character of these materials. Deviations of the sum rule for ${\mathrm{MnF}}_{2}$ from the ionic exchange interaction are taken as evidence that satellite structure present in the photoemission spectra may not have been identified.

The interplay between the resonant Raman and the Auger-like regime across the Cu 2p→3d absorption threshold was investigated. The resonant photoemission experiment performed on CuGeO 3 unambiguously shows that a fraction of primary electrons is contributing to the interfering resonant Raman emission even when the noninterfering Cu L 3 M 4 , 5 M 4 , 5 Auger emission is clearly detectable. At the 2p→3d resonance the autoionization channel prevails over the direct photoemission channel and, in agreement with the Fano theory, a high q value (9′2) was extracted from the data by properly tracking the weak resonant emission above the absorption threshold.

The structure of thin silver films, grown under varying conditions of ion bombardment, are compared by means of their measured structural, optical, and electrical properties. Both the x-ray diffraction results and the dielectric-function measurements suggested that there are voids in our films and that their volume fraction depends on the energy delivered to the substrate during growth. Furthermore, the same dependency on energy was found for the amount of gas atoms trapped in the films, but the low percentage suggests that this cannot have a major influence on the structure or other properties. However, the gas atoms can contribute to an expansion of the lattice by increasing the separation of the metallic grains and increasing the volume fraction of voids. The dc electrical conductivity was interpreted from the microstructure and optical data with a model including scattering at grain boundaries, the fraction of voids and the bulk conductivity. In particular, a comparison between theoretical and experimental data suggest that the electron reflection coefficient at the grain surfaces is not constant, but depends on the condition of film growth.