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The ternary rare-earth metal fluoride CsEuF3 adopts an ideal cubic perovskite structure [ABX3] under ambient conditions. The B-cation site is occupied by the rare-earth Eu ion and EuF6 octahedra are formed. In the present study, magnetic susceptibility and synchrotron X-ray absorption spectroscopy (XAS) analysis at the Eu- L3 edge confirmed that Eu is in a divalent oxidation state under ambient conditions. Temperature-dependent magnetic susceptibility data revealed that the average Eu valence increased below 20 K due to a partial transition from the Eu2+ state to the Eu3+ state, thereby resulting in a mixed valence state with an average valence of +2.23. Direct evidence for valence fluctuation by the Eu ions in CsEuF3 was obtained using the high pressure high energy resolution fluorescence detection-XAS technique, where continuous changes in valence were observed from 2.15+ at ambient pressure up to 2.5+ at 10.5 GPa. These findings indicate the possibility of discovering interesting physical properties associated with valence instabilities by rare-earth metals in similar systems.

The hydrostatic pressure dependent evolution of the electronic and magnetic structure of LaCo

Non-Fermi-liquid (NFL), a significant deviation from Fermi-liquid theory, usually emerges near an order-disorder phase transition at absolute zero. Recently, a diverging susceptibility toward zero temperature was observed in a quasicrystal (QC). Since an electronic long-range ordering is normally absent in QCs, this anomalous behaviour should be a new type of NFL. Here we study high-resolution partial-fluorescence-yield x-ray absorption spectroscopy on Yb-based intermediate-valence icosahedral QCs and cubic approximant crystals (ACs), some of which are new materials, to unveil the mechanism of the NFL. We find that for both forms of QCs and ACs, there is a critical lattice parameter where Yb-valence and magnetism concomitantly exhibit singularities, suggesting a critical-valence-fluctuation-induced NFL. The present result provides an intriguing structure–property relationship of matter; size of a Tsai-type cluster (that is a common local structure to both forms) tunes the NFL whereas translational symmetry (that is present in ACs but absent in QCs) determines the nature of the NFL against the external/chemical pressure.

Plasmon is a collective excitation of electrons in materials. Since plasmon can be observed in a wide range of the phase diagram including the solid, liquid, and classical plasma phases, the investigation of the electronic states through the plasmon is of great significance in order to obtain a unified insight into the electronic states in various phases of matter. Inelastic X-ray scattering (IXS) is an ideal tool for such an investigation, because it can be applied to the samples in the liquid state and those in an extreme conditions. In this review, we discuss IXS results on the plasmons in liquid metals, and also describe a formulation to predict the plasmon energy and the lifetime in liquid metals. The formulation takes into account the effect of the ionic structure within the nearly free electron approximation, and reproduces well the experimental results.

(Sm1/3Ca2/3)2.75C60 is a member of the family of non-stoichiometric strongly-correlated rare-earth fullerides, (Sm1−xCax)2.75C60 (0 ≤ x ≤ 1), in which an orthorhombic 2 × 2 × 2 supercell of the face-centred cubic (fcc) unit cell of stoichiometric A3C60 (A = alkali metal) fullerides is stabilized by the long-range ordering of partially-occupied metal sites. At ambient temperature and pressure, it is a mixed valence compound with an average Sm valence of +2.33(2) implying a formal charge of −5.78 for the C60 anions. Here we study its electronic response to the application of pressure in the range 0–9 GPa. Synchrotron X-ray absorption measurements in the high-resolution partial fluorescence yield mode (PFY-XAS) at ambient temperature show the onset of an abrupt strongly hysteretic (width ∼2.5 GPa) first-order reversible phase transition at ∼4 GPa, accompanied by a drastic increase in the bulk Sm valence by ∼20% to +2.71(3). This is coincident with the huge lattice contraction and concomitant insulator-to-metal transition encountered before for Sm2.75C60 in the same pressure range and provides a possible explanation of the physical properties in terms of the strong coupling between the lattice and electronic degrees of freedom. The behaviour is reminiscent of the electronic and lattice response to pressure of highly correlated Kondo insulators like SmS and its ternary derivatives, Sm1−xRxS (R = Ca, Y, etc.). However, a distinguishing feature of the fulleride systems is that the C60 anionic sublattice can act as an electron reservoir due to the availability of a close-lying band derived by the t1g orbitals and can accept excess charge as the 4f-electron occupation number decreases. The observed electronic response as a function of pressure is thus opening new possibilities for accessing metallic fullerides at elevated pressures.

Reducing noble-metal loading and improving the oxygen reduction reaction (ORR) performance are two of the most important topics in developing a cost-effective fuel cell system. In this study, nanocatalysts (NCs) comprising NiOx supported Pd nano-islands and a sub-nanometer Pt cluster mask (NPP) are developed. We demonstrate that the oxide structure can be suppressed along with the increase of Ni intermixed by decorating with an appropriate amount of Pt cluster mask on the surface, thus boosting the ORR performance of NPP NCs. In the optimum case, with a Pt loading of 9 wt%, the Pt decorated Ni@Pd NC showed an increase in mass activity of ∼22.74-fold (1523.7 mA mg−1) and ∼26.8-fold (671.5 mA mg−1), compared to that of the commercial Pt catalyst at 0.85 volt (vs. RHE) (67.1 mA mg−1) and 0.90 volt (vs. RHE) (24.5 mA mg−1), respectively. Such an optimization can be attributed to the proper control of the surface coverage and size of the Pt clusters. This protects the surface from oxidation, thus leaving a high density of reaction sites for oxygen adsorption in the ORR. Further increasing the Pt content results in a high density of nucleation sites and a high extent of homoatomic clustering of the Pt atoms on the NiOx@Pd surface. Such a scenario reduces the surface coverage of Pt clusters and, in this event, suppresses the ORR activity of NPP NCs. The result obtained in this study is very exciting and is an important clue for the development of next-generation ORR catalysts.

The promoting effect of cobalt on the catalytic activity of a NiCoO Dry Methane Reforming (DMR) catalyst was studied by a combination of in situ Kβ X-ray Emission Spectroscopy (XES) and Kβ-detected High Energy Resolution Fluorescence Detected X-ray absorption spectroscopy (HERFD XAS). Following the calcination process, Ni XES and Kβ-detected HERFD XAS data revealed that the NiO coordination in the NiCoO catalyst has a higher degree of symmetry and is different than that of pure NiO/γ-Al2O3. Following the reductive activation, it was found that the NiCoO/γ-Al2O3 catalyst required a relatively higher temperature compared to the monometallic NiO/γ-Al2O3 catalyst. This finding suggests that Co is hampering the reduction of Ni in the NiCoO catalyst by modulation of its electronic structure. It has also been previously shown that the addition of Co enhances the DMR activity. Further, the Kβ XES spectrum of the partly reduced catalysts at 450 °C reveals that the Ni sites in the NiCoO catalyst are electronically different from the NiO catalyst. The in situ X-ray spectroscopic study demonstrates that reduced metallic Co and Ni are the primary species present after reduction and are preserved under DMR conditions. However, the NiCo catalyst appears to always be somewhat more oxidized than the Ni-only species, suggesting that the presence of cobalt modulates the Ni electronic structure. The electronic structural modulations resulting from the presence of Co may be the key to the increased activity of the NiCo catalyst relative to the Ni-only catalyst. This study emphasizes the potential of in situ X-ray spectroscopy experiments for probing the electronic structure of catalytic materials during activation and under operating conditions.

Phosphide-based electrocatalysts exhibit high activities in alkaline solution toward overall water electrolysis. However, their real phases during catalysis have not been comprehensively identified...

We examine electronic and crystal structures of iron-based superconductors

Microstructure and morphology of particles play key roles in optimizing the properties of shape-selected ZnO particles, which are essential factors for flexible and reliable applications. In particular, chemical understanding and physical measurement with scientific theory must be further integrated for the realization of finely tuned ZnO nano/microstructures with desired sizes and shapes. Herein, we deliver a detailed description of the mechanism that mimics the formation of finely-tuned, spherical ZnO nanoparticles (NPs) at the computational level. We tackled issues that significantly affect the favorable structural motifs of the spherical ZnO NPs grown hydrothermally from ethanolic solution leading to their advancing chemical and physical properties. The excellent photocatalytic activity of the spherical ZnO was addressed by an apparent-rate constant of 9.7(2)x10-2 min-1 efficiently degrading the Rhodamine B solution by ∼99% in 50 min. The apparent-rate constant for tubular ZnO particles is almost six times lower than that of spherical ZnO NPs. Comparative results revealed that the diversity of size and shape of ZnO particles distinguishes the wurtzite-to-rocksalt transformation reversibility phenomena by dictating the microstructure-dependent deformation behavior and ultimately leading to different transition-induced elastic strain responses to hydrostatic pressure up to 30 GPa.

The pressure-induced change in the electronic structures of the superconductors ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ and ${\mathrm{Ag}}_{x}{\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ has been measured with high-resolution x-ray absorption spectroscopy. As a common feature for these compounds, we find that pressure causes the broadening of the Se $4p$ band and an energy shift of the Bi $6s$ band above the Fermi level up to the pressure of the first structural transition. These results, corroborated by density functional theory calculations, correlate with an increase of the carrier density, the disappearance of the band gap, and the emergence of superconductivity. The electronic structure changes significantly at the pressure of the first structural transition, which may be a trigger of the emergence of superconductivity, while above the pressure of the first phase transition it does not change much even around the second phase transition pressure, corresponding to the nearly constant ${T}_{\mathrm{c}}$ above the pressure of the second structural transition.

We have measured the momentum distribution and renormalization factor ${Z}_{{k}_{F}}$ in liquid and solid lithium by high-resolution Compton scattering. High-resolution data over a wide momentum range exhibit a clear feature of the renormalization and a sharp drop of momentum densities at the Fermi momentum ${k}_{F}$. These results are compared with those computed by quantum Monte Carlo simulation performed both on a disordered crystal and a liquid exhibiting very good agreement. Asymptotic behavior of the experimental and theoretical momentum distributions are examined to estimate ${Z}_{{k}_{F}}$. The experimentally obtained ${Z}_{{k}_{F}}=0.{43}_{\ensuremath{-}0.01}^{+0.11}$ for liquid Li and $0.{54}_{\ensuremath{-}0.02}^{+0.11}$ for solid Li are in good agreement with theoretical results of $0.54\ifmmode\pm\else\textpm\fi{}0.01$ and $0.64\ifmmode\pm\else\textpm\fi{}0.01$, respectively.

One challenge in studying high-temperature superconductivity (HTSC) stems from a lack of direct experimental evidence linking lattice inhomogeneity and superconductivity. Here, we apply synchrotron hard X-ray nanoimaging and small-angle scattering to reveal a novel micron-scaled ribbon phase in optimally doped Bi2Sr2CaCu2O8+δ (Bi-2212, with δ = 0.1). The morphology of the ribbon-like phase evolves simultaneously with the dome-shaped TC behavior under pressure. X-ray absorption studies show that the increasing of TC is associated with oxygen-hole redistribution in the CuO2 plan, while TC starts to decrease with pressure when oxygen holes become immobile. Additional X-ray irradiation experiments reveal that nanoscaled short-range ordering of oxygen vacancies could further lower TC, which indicates that the optimal TC is affected not only by an optimal morphology of the ribbon phase, but also an optimal distribution of oxygen vacancies. Our studies thereby provide for the first time compelling experimental e...

We examine electronic and crystal structures of iron-based superconductors LnFeAsO1−x H x (Ln = La, Sm) under pressure by means of x-ray absorption spectroscopy (XAS), x-ray emission spectroscopy (XES), and x-ray diffraction. In LaFeAsO the pre-edge peak on high-resolution XAS at the Fe-K absorption edge gains in intensity on the application of pressure up to 5.7 GPa and it saturates in the higher pressure region. We found integrated-absolute difference values on XES for Ln = La, corresponding to a spin state, decline on the application of pressure, and then it is minimized when the T c approaches the maximum at around 5 GPa. In contrast, such the optimum value was not detected for Ln = Sm. We reveal that the superconductivity is closely related to the lower spin state for Ln = La unlike Sm case. We observed that As height from the Fe basal plane and As–Fe–As angle on the FeAs4 tetrahedron for Ln = La deviate from the optimum values of the regular tetrahedron in superconducting (SC) phase, which has been widely accepted structural guide to SC thus far. In contrast, the structural parameters were held near the optimum values up to ∼15 GPa for Ln = Sm.

The nature of the non-magnetic to paramagnetic transition of Co3+ oxide LaCoO3 was strongly disputed in the literature for many decades from a low-spin (LS) state below 20 K and to a mixed LS state and high-spin (HS) state or an intermediate-spin (IS) state above 100 K. In this context, the layered perovskite LaSrCoO4 is more favorable for a Jahn-Teller-active IS state because of an elongated distortion, but has been scarcely studied with experimental X-ray spectroscopies as a function of temperature or external pressure. Here, our Co-L2,3 X-ray absorption spectroscopic study indicates a mixture of 40% HS-Co3+ and 60% LS-Co3+ for LaSrCoO4 against 25% HS-Co3+ and 75% LS-Co3+ for LaCoO3 at 300 K and ambient pressure (AP). At 10 K, we observed a sizable magnetic-circular-dichroism signal and a clear HS state of the magnetic Co3+ ion from the Co-L2,3 edge of LaSrCoO4. This result demonstrates that the HS state is already populated in the ground state versus a pure LS ground state in LaCoO3. A quantitative change of quantum number of the spin of the Co3+ ion of LaSrCoO4 as a function of pressure and temperature investigated systematically with Co-Kβ X-ray emission experiments firmly demonstrates not only a mixed state of LS/HS at 300 K and AP but also a presence of the pure LS-Co3+ and HS-Co3+ states only under high pressure and high temperature, respectively.

We applied X-ray Raman scattering technique to MgSiO3 glass, a precursor to magnesium silicate melts, with respect to magnesium and silicon under high-pressure conditions as well as some polycrystalline phases of MgSiO3 at ambient conditions. We also performed ab initio calculations to interpret the X-ray Raman spectra. Experimentally obtained silicon L-edge spectra indicate that the local environment around silicon started changing at pressure above 10 GPa, where the electronic structure of oxygen is known to change. In contrast, the shape of the magnesium L-edge spectrum changed below 10 GPa. This indicates that the magnesium sites in MgSiO3 glass first distort and that the local structure around magnesium shows a wide variation under pressure. The framework structure consisting of silicon and oxygen changed above 10 GPa, where the coordination number of silicon was more than four. Our results imply that 6-oxygen-coordinated silicon was formed above 20 GPa.

In this study an analysis strategy towards using the resonant inelastic X-ray scattering (RIXS) technique more effectively compared with X-ray absorption spectroscopy (XAS) is presented. In particular, the question of when RIXS brings extra information compared with XAS is addressed. To answer this question the RIXS plane is analysed using two models: (i) an exciton model and (ii) a continuum model. The continuum model describes the dipole pre-edge excitations while the exciton model describes the quadrupole excitations. Applying our approach to the experimental 1s2p RIXS planes of VO2 and TiO2, it is shown that only in the case of quadrupole excitations being present is additional information gained by RIXS compared with XAS. Combining this knowledge with methods to calculate the dipole contribution in XAS measurements gives scientists the opportunity to plan more effective experiments.

High-resolution partial-fluorescence-yield X-ray absorption and resonant X-ray emission spectra were used to characterize the temperature dependence of Sm 4f configurations and orbital/charge degree of freedom in SmB6. The variation of Sm 4f configurations responds well to the formed Kondo gap, below 140 K, and an in-gap state, below 40 K. The topological in-gap state is correlated with the fluctuating population of Sm 4f configurations that arises via carrier transfer between 3d94f6 and 3d94f5 states; both states are partially delocalized, and the mediating 5d orbital plays the role of a transfer path. Complementary results shown in this work thus manifest the importance of configuration fluctuations and orbital delocalization in the topological surface state of SmB6.

We argue that the magnetic circular dichroism (MCD) of the hard x-ray Raman scattering (XRS) could be used as an element selective probe of local spin polarization. The magnitude of the XRS-MCD signal is directly proportional to the local spin polarization when the angle between the incident wavevector and the magnetization vector is $135^{\circ}$ or $-45^{\circ}$. By comparing the experimental observation and the configuration interaction calculation at the $L_{2,3}$ and $M_{2,3}$ edges of ferromagnetic iron, we suggest that the integrated MCD signal in terms of the transferred energy could be used to estimate the local spin moment even in the case where the application of the spin sum-rule in X-ray absorption is questionable. We also point out that XRS-MCD signal could be observed at the $M_{1}$ edge with a magnitude comparable to that at the $M_{2,3}$ edge, although the spin-orbit coupling is absent in the core orbital. By combining the XRS-MCD at various edges, spin polarization distribution depending on the orbital magnetic quantum number would be determined., Comment: 22 pages, 7 figures

Hyperhoneycomb iridate $\ensuremath{\beta}\ensuremath{-}{\mathrm{Li}}_{2}{\mathrm{IrO}}_{3}$ is a three-dimensional analog of two-dimensional honeycomb iridates, such as $\ensuremath{\alpha}\ensuremath{-}{\mathrm{Li}}_{2}{\mathrm{IrO}}_{3}$, which recently appeared as another playground for the physics of Kitaev-type spin liquid. $\ensuremath{\beta}\ensuremath{-}{\mathrm{Li}}_{2}{\mathrm{IrO}}_{3}$ shows a noncollinear spiral ordering of spin-orbital-entangled ${J}_{\mathrm{eff}}=1/2$ moments at low temperatures below 38 K, which is known to be suppressed under a pressure of $\ensuremath{\sim}2$ GPa. In addition, a structural transition is observed at ${P}_{\mathrm{S}}\ensuremath{\sim}4$ GPa at room temperature. Using the neutron powder diffraction technique, the crystal structure in the high-pressure phase of $\ensuremath{\beta}\ensuremath{-}{\mathrm{Li}}_{2}{\mathrm{IrO}}_{3}$ above ${P}_{\mathrm{S}}$ was refined, which indicates the formation of ${\mathrm{Ir}}_{2}$ dimers on the zigzag chains, with an Ir-Ir distance of $\ensuremath{\sim}2.66\phantom{\rule{0.16em}{0ex}}\AA{}$, even shorter than that of metallic Ir. We argue that the strong dimerization stabilizes the bonding molecular-orbital state comprising the two local ${d}_{zx}$ orbitals in the Ir-${\mathrm{O}}_{2}$-Ir bond plane, which conflicts with the equal superposition of ${d}_{xy}, {d}_{yz}$, and ${d}_{zx}$ orbitals in the ${J}_{\mathrm{eff}}=1/2$ wave function produced by strong spin-orbit coupling. The results of resonant inelastic x-ray scattering measurements and the electronic structure calculations are fully consistent with the collapse of the ${J}_{\mathrm{eff}}=1/2$ state. The competition between the spin-orbital-entangled ${J}_{\mathrm{eff}}=1/2$ state and molecular-orbital formation is most likely universal in honeycomb-based Kitaev materials.

We report the high-pressure behavior of plasmon in polycrystalline Li up to 15 GPa at room temperature studied by inelastic x-ray scattering and ab initio calculation. The plasmon energy () increases with decreasing atomic volume (), and the slope exhibits a discontinuity at bcc → fcc structural phase boundary reflecting the electronic band structure change. The plasmon peak width () versus momentum transfer (q) curve of bcc-Li below 6.5 GPa keeps similar parabola-like shape. Above 8.4 GPa, where Li is in fcc, it changes from that of bcc-Li and has a convex shape., A B acknowledges financial support from the Spanish Ministry of Economy and Competitiveness (FIS2016-76617-P) and the Department of Education, Universities and Research of the Basque Government and the University of the Basque Country (IT756-13).

Composite electrocatalysts have exhibited high activities toward water electrolysis, but the catalytically active sites really in charge of the reaction are still debatable while the conventional in situ X-ray spectroscopies are not capable of conclusively identifying the interaction of these materials with the electrolyte because of the complexity of catalysis. In this work, by utilization of operando Kβ1,3 high-energy resolution fluorescence-detected X-ray absorption spectroscopy (HERFD-XAS) with a small incident angle, the operando quadrupole transition obviously showed that oxygen directly interacted with 3d orbitals of Co ions rather than that of Fe ions. Most importantly, Fe ions can promote the stabilization of the Co ions under a higher valent state during water oxidation, which may lead to a stable intermediate of reactant and its superior intrinsic activity. Accompanied by the first-principle calculations, the intermediates between 3d orbitals for surface Co ions and O 2p orbitals for the attach...

Rare-earth (RE) fullerides are an intriguing family of materials in which electronic instabilities on the RE sublattice couple to the electronic and lattice degrees-of-freedom of the strongly-correlated fulleride sublattice. In particular, insulating Sm2.75C60 adopts an orthorhombic superstructure, arising from long-range ordering of Sm partial vacancies, and can be driven to a lattice-collapsed metallic state due to a valence transition towards Sm3+ upon pressurization. Here we use synchrotron X-ray absorption spectroscopy (XAS) at the Sm L3 edge at ambient conditions to authenticate the mixed valence character of the material by identifying two features due to distinct Sm2+ and Sm3+ components – their relative intensity allows a direct measure of the average Sm valence in Sm2.75C60 at +2.07(3). We then attempt to mimic the physical pressure effect on the electronic properties by co-intercalation of the smaller-size valence-precise Ca2+ ion to form the series of ternary solid solutions, (Sm1-xCax)2.75C60 (0 ≤ x ≤ ⅔). XAS measurements in their high-resolution partial fluorescence yield (PFY) variance find that chemical pressure leads to an increase of the Sm3+ contribution to the average valence by >10% in the most contracted member, (Sm⅓Ca⅔)2.75C60 of the present study with the average valence reaching a value of +2.33(2). Assuming full charge transfer between the metal ions and C60, the charge on the C60 units remains invariant throughout at approximately −5.78. This opens the possibility that the system can be tuned further towards the higher average valences needed for the high-pressure insulator-to-metal transition in Sm2.75C60 to be shifted to ambient pressure with a single-valence Sm3+ state accessible at a Ca content of x ~0.9.

Diopside, CaMgSi2O6, is an important analogue for depolymerized silicate melts. We have used the complimentary spectroscopies, X-ray Raman Scattering (XRS), X-ray absorption near edge structure (XANES) and Raman, to investigate diopside glass in situ to 20 GPa. We observe a stark change in behavior of CaMgSi2O6 near 4 GPa that corresponds to a major change in the rate of inter-tetrahedral angle (∠Si–O–Si) closure. Below 4 GPa, the ∠Si–O–Si closes rapidly at 2–3°/GPa whereas above 4 GPa it decreases by ∼1°/GPa. A distinct shift to higher wavenumbers of the 870 and 905 cm−1 Raman bands are observed at 1.3 GPa suggesting that Q0 species have been completely converted to Q1 or higher Qn species. XRS measurements at the O K-edge suggest that [5]Si is formed by 3 GPa. This formation is accompanied by a rapid decrease in the ∠Si–O–Si and a decrease in Q0 species. A linear increase in the geometric mean of the high frequency envelope, the χ b value, from 999 to 1018 cm−1 suggests that the conversion of NBO to BO is continuous up to 14 GPa. Above 14 GPa, the Raman spectra show an obvious negative shift in both, the high frequency peak maximum, and the χ b position. Simultaneously, the low frequency envelope looses its asymmetry at 14 GPa. This may be explained by either a loss of a vibrational mode in the range 1000–1200 cm−1 and/or the formation of [6]Si. The structural evolution of CaMgSi2O6 correlates well with a major change in the compressibility and diffusivity around 5 GPa.

One challenge in studying high-temperature superconductivity (HTSC) stems from a lack of direct experimental evidence linking lattice inhomogeneity and superconductivity. Here, we apply synchrotron hard X-ray nanoimaging and small-angle scattering to reveal a novel micron-scaled ribbon phase in optimally doped Bi

The electronic structure of ${\mathrm{YbCu}}_{4.5}$ under pressure has been studied with x-ray emission spectroscopy. Pressure-induced first-order valence transition to the divalent Yb state is found around 0.6--2.7 GPa, accompanied by the structural transition at the same pressure range of 0--1.0 GPa suggested by the change in the x-ray diffraction pattern. We also measured temperature dependencies of the Yb valence and magnetic susceptibility, which are compared with the single impurity Anderson model.

Electronic structures of ferromagnetic heavy fermion Yb compounds of YbPdSi, YbPdGe, and YbPtGe are studied by photoelectron spectroscopy around the Yb 4d-4f resonance, resonant x-ray emission spectroscopy at the Yb L 3 absorption edge, and density functional theory combined with dynamical mean field theory calculations. These compounds all have a temperature-independent intermediate Yb valence with large [Formula: see text] and small [Formula: see text] components. The magnitude of the Yb valence is evaluated to be YbPtGe [Formula: see text] YbPdGe [Formula: see text] YbPdSi, suggesting that YbPtGe is the closest to the quantum critical point among the three Yb compounds. Our results support the scenario of the coexistence of heavy fermion behavior and ferromagnetic ordering which is described by a magnetically-ordered Kondo lattice where the magnitude of the Kondo effect and the RKKY interaction are comparable.

The collective electronic excitations and their dispersion behavior across both the first and second Brillouin zones in a bulk $\mathrm{Mo}{\mathrm{S}}_{2}$ single crystal have been investigated using nonresonant inelastic hard x-ray scattering and time-dependent density-functional theory. The experiment results revealed two main plasmons located around 8.6 and 23 eV. The $\ensuremath{\sim}8.6\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$ plasmon shows clear anisotropic behavior and was only observed in plane due to the two-dimensional geometry. In addition, theoretical calculation indicates that the dispersion behavior of this in-plane plasmon shows weak momentum dependence. The main plasmon near 23 eV demonstrates an isotropic three-dimensional collective electron excitation behavior, which suggests a weak correlation between the electron excitation and layered lattice structure. This behavior is completely different from the anisotropic dispersion behavior found in layered graphite. Our work provides clear experimental and theoretical data on the dynamic electronic behavior of excited high-energy electrons in $\mathrm{Mo}{\mathrm{S}}_{2}$, which not only provides guidance on device design but also furthers understanding of electronic behaviors in other similar systems.

High-resolution partial-fluorescence-yield X-ray absorption and resonant X-ray emission spectra were used to characterize the temperature dependence of Sm 4f configurations and orbital/charge degree of freedom in SmB