Search

We used Inelastic X-ray Scattering to gain insight into the complex Terahertz dynamics of a diluted Au-nanoparticles suspension in glycerol. We observe that, albeit sparse, Au-nanoparticles leave clear signatures on the dynamic response of the system, the main one being an additional mode propagating at the nanoparticle-glycerol interface. A Bayesian inferential analysis of the lineshape reveals that such a mode, at variance with conventional acoustic modes, keeps a hydrodynamic-like behavior well beyond the continuous limit and down to sub-nanometer distances.

International audience; We used the high-resolution Inelastic X-ray Scattering beamline of the Advanced Photon Source at Argonne National Laboratory to measure the terahertz spectrum of pure water and a dilute aqueous suspension of 15 nm diameter spherical Au nanoparticles (Au-NPs). We observe that, despite their sparse volume concentration of about 0.5%, the immersed NPs strongly influence the collective molecular dynamics of the hosting liquid. We investigate this effect through a Bayesian inference analysis of the spectral lineshape, which elucidates how terahertz transport properties of water change upon Au-NP immersion. In particular, we observe a nearly complete disappearance of the longitudinal acoustic mode and a mildly decreased ability to support shear wave propagation.

We consider here the possibility of shaping the high-frequency acoustic propagation in a liquid upon directional confinement. This hypothesis is investigated by Inelastic X-ray Scattering measurements on water confined in aligned multi-walled carbon nanotubes, in which the momentum transfer was either parallel or orthogonal to the confinement axis. The comparison between the spectra measured in these two scattering geometries highlights the anisotropic nature of the dynamic response of directionally confined water, thus potentially inspiring new pathways to shape high-frequency sound propagation in isotropic systems. Finally, a Bayesian analysis of measured spectra unravels close similarities in the phonon dispersions of multiwalled nanotubes and graphite.

Significance Although it is believed that the raft formation in a cell membrane is governed by a selective interaction of different lipids and proteins, mechanisms driving and regulating the lateral membrane heterogeneity remain poorly understood. Here, using multicomponent lipid mixtures and inelastic X-ray scattering, we provide a spatial–temporal window to study lipid–lipid interactions. We show experimental evidence for the formation of dynamic lipid pairs, which are subnanometer in size and have a subnanosecond lifetime. These pairs form transient nanoscopic substructures in the liquid-ordered phase. The presented approach to study membrane heterogeneity is universal and can be applied to more realistic lipid mixtures, offering the possibility to discern differences between the structures of ordered and disordered phases in a cell membrane., Biological membranes exhibit a great deal of compositional and phase heterogeneity due to hundreds of chemically distinct components. As a result, phase separation processes in cell membranes are extremely difficult to study, especially at the molecular level. It is currently believed that the lateral membrane heterogeneity and the formation of domains, or rafts, are driven by lipid–lipid and lipid–protein interactions. Nevertheless, the underlying mechanisms regulating membrane heterogeneity remain poorly understood. In the present work, we combine inelastic X-ray scattering with molecular dynamics simulations to provide direct evidence for the existence of strongly coupled transient lipid pairs. These lipid pairs manifest themselves experimentally through optical vibrational (a.k.a. phononic) modes observed in binary (1,2-dipalmitoyl-sn-glycero-3-phosphocholine [DPPC]–cholesterol) and ternary (DPPC–1,2-dioleoyl-sn-glycero-3-phosphocholine/1-palmitoyl-2-oleoyl-glycero-3-phosphocholine [DOPC/POPC]–cholesterol) systems. The existence of a phononic gap in these vibrational modes is a direct result of the finite size of patches formed by these lipid pairs. The observation of lipid pairs provides a spatial (subnanometer) and temporal (subnanosecond) window into the lipid–lipid interactions in complex mixtures of saturated/unsaturated lipids and cholesterol. Our findings represent a step toward understanding the lateral organization and dynamics of membrane domains using a well-validated probe with a high spatial and temporal resolution.

In recent years, responsive polymer-based structures have been studied extensively due to their unique ability to alter their physical properties upon exposure to external stimuli. Despite this, the nanoscale Q-resolved dynamic properties of these materials have barely been explored, which is limiting the development and applications of these materials. To address this issue, we used inelastic X-ray scattering (IXS) and found evidence for van der Waals mediated molecular vibration-responsive rattling dynamics in bulk poly(isoprene-block-styrene) (SI) and poly(styrene-block-ethylene oxide) (SO) stacked thin film block copolymers. Their cylinder-forming hexagonally arranged static structures were characterized using small-angle X-ray scattering (SAXS) and grazing incidence small-angle X-ray scattering (GISAXS), complemented by scanning electron microscopy (SEM). Specifically, we observed that the longitudinal vibrational mode in bulk SI experiences a strong phonon attenuation as temperature increases from 3...

The control of phonon propagation in nanoparticle arrays is one of the new frontiers of nanotechnology, potentially enabling the discovery of materials with unknown functionalities for potential innovative applications. The exploration of the terahertz window appears quite promising as phonons in this range are the leading carriers of heat transport in insulators and their control is the key to implement devices for heat flow management. Unfortunately, this scientific field is still in its infancy and even a basic topic such as the influence of floating nanoparticles on the terahertz phonon propagation of a colloidal suspension still eludes a firm answer. Shedding some light on this topic is the main motivation of the present work, which focuses an Inelastic X-Ray Scattering (IXS) measurements on a dilute suspension of Au nano-spheres in water. Measured spectra showed a non-trivial and unexpected shape displaying multiple inelastic features that, based on a Bayesian inference analysis, we assign to phonon modes propagating throughout the nanoparticle interior. Surprisingly, the spectra bear no evidence of propagating modes, which are known to dominate the spectrum of pure water, owing to the scattering that these modes suffer from the sparse nanoparticles in suspension. In perspective, this finding may inspire simple routes to manipulate high-frequency acoustic propagation in hybrid - liquid and solid- materials.

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...

The investigation of phononic collective excitations in soft matter systems at the molecular scale has always been challenging due to limitations of experimental techniques in resolving low-energy modes. Recent advances in inelastic X-ray scattering (IXS) enabled the study of such systems with unprecedented spectral contrast at meV excitation energies. In particular, it has become possible to shed light on the low-energy collective motions in materials whose morphology and phase behavior can easily be manipulated, such as mesogenic systems. The understanding of collective mode behavior with a Q-dependence is the key to implement heat management based on the control of a sample structure. The latter has great potential for a large number of energy-inspired innovations. As a first step toward this goal, we carried out high contrast IXS measurements on a liquid crystal sample, D7AOB, which exhibits solid-like dynamic features, such as the coexistence of longitudinal and transverse phononic modes. For the first time, we found that these terahertz phononic excitations persist in the crystal, smectic A, and isotropic phases. Furthermore, the intermediate smectic A phase is shown to support a van der Waals-mediated nonhydrodynamic mode with an optical-like phononic behavior. The tunability of the collective excitations at nanometer-terahertz scales via selection of the sample mesogenic phase represents a new opportunity to manipulate optomechanical properties of soft metamaterials.

In this work we report on terahertz phononic excitations in two-dimensional (2D) gold nanoparticle arrays in a water matrix through a series of large-scale molecular dynamics simulations. For the first time, we observe acoustic Dirac-like crossings in H (H2O) atomic (molecular) networks that emerge due to an intraband phononic scattering. These crossings are the phononic fingerprints of ice-like arrangements of H (H2O) atomic (molecular) networks at nanometer scale. We reveal how phononic excitations in metallic nanoparticles and the water matrix reciprocally impact on one another providing the mechanism for the THz phononics manipulation via structural engineering. Furthermore, we show that by tuning the arrangement of 2D gold nanoparticle assemblies, the Au phononic polarizations experience subterahertz hybridization (Kohn anomaly) due to surface electron–phonon relaxation processes. This opens the way for the sound control and manipulation in soft matter metamaterials at nanoscale.

Nearly two decades of thorough inelastic X-ray scattering (IXS) studies of transverse-like excitation in the spectrum of simple amorphous materials are reviewed. Particular attention is given to the case of liquid water and other prototypical samples, through discussion of both solved and still open issues. The perspectives opened up by the development of next generation IXS instruments with unprecedented contrast and resolution bandwidth are briefly illustrated.

In this work, we report on inelastic X-ray scattering experiments combined with the molecular dynamics simulations on deeply supercritical Ar. The presented results unveil the mechanism and regimes of sound propagation in the liquid matter and provide compelling evidence for the adiabatic-to-isothermal longitudinal sound propagation transition. We introduce a Hamiltonian predicting low-frequency transverse sound propagation gaps, which is confirmed by experimental findings and molecular dynamics calculations. As a result, a universal link is established between the positive sound dispersion (PSD) phenomenon and the origin of transverse sound propagation revealing the viscous-to-elastic crossover in liquids. The PSD and transverse phononic excitations evolve consistently with theoretical predictions. Both can be considered as a universal fingerprint of the dynamic response of a liquid, which is also observable in a subdomain of supercritical phase. The simultaneous disappearance of both these effects at elevated temperatures is a manifestation of the Frenkel line. We expect that these findings will advance the current understanding of fluids under extreme thermodynamic conditions., Comment: 18 pages, 5 figures

High-quality quartz (α-SiO2) crystals are characterized, and their use for inelastic X-ray scattering analyzers is presented and discussed., Spherical analyzers are well known instruments for inelastic X-ray scattering (IXS) experiments. High-resolution IXS experiments almost always use Si single crystals as monochromators and spherical analyzers. At higher energies (>20 keV) Si shows a high energy resolution (

A concept of an inelastic x-ray scattering (IXS) spectrograph with an imaging analyzer was proposed recently and discussed in a number of publications (see e.g. Ref.1). The imaging analyzer as proposed combines x-ray lenses with highly dispersive crystal optics. It allows conversion of the x-ray energy spectrum into a spatial image with very high energy resolution. However, the presented theoretical analysis of the spectrograph did not take into account details of the scattered radiation source, i.e. sample, and its impact on the spectrograph performance. Using numerical simulations we investigated the influence of the finite sample thickness, the scattering angle and the incident energy detuning on the analyzer image and the ultimate resolution.

A novel on-axis X-ray microscope with 3 µm resolution, 3x magnification, and a working distance of 600 mm for in-situ sample alignment and X-ray beam visualization for the Inelastic X-ray Scattering (IXS) beamline at NSLS-II is presented. The microscope uses reflective optics, which minimizes dispersion, and allows imaging from Ultraviolet (UV) to Infrared (IR) with specifically chosen objective components (coatings, etc.). Additionally, a portable high resolution X-ray microscope for KB mirror alignment and X-ray beam characterization was developed.

The passive transport of molecules through a cell membrane relies on thermal motions of the lipids. However, the nature of transmembrane transport and the precise mechanism remain elusive and call for a comprehensive study of phonon excitations. Here we report a high resolution inelastic X-ray scattering study of the in-plane phonon excitations in 1,2-dipalmitoyl-sn-glycero-3-phosphocholine above and below the main transition temperature. In the gel phase, for the first time, we observe low-frequency transverse modes, which exhibit a phonon gap when the lipid transitions into the fluid phase. We argue that the phonon gap signifies the formation of short-lived nanometre-scale lipid clusters and transient pores, which facilitate the passive molecular transport across the bilayer plane. Our findings suggest that the phononic motion of the hydrocarbon tails provides an effective mechanism of passive transport, and illustrate the importance of the collective dynamics of biomembranes., The molecular transport through bio-membranes of cells heavily relies on the dynamics of lipids, but the related mechanism remains unknown. Here, Zhernenkov et al. observe the propagating transverse phonon mode with a finite band gap and suggest its connection to short-lived local lipid clustering.

The principles of the virtual source spread (spatial broadening) phenomenon induced by angular dispersion in asymmetric X-ray Bragg reflections are illustrated, from which the virtual source properties are analyzed for typical high-resolution multiple-crystal monochromators, including inline four-bounce dispersive monochromators, back-reflection-dispersion monochromators and nondispersive nested channel-cut monochromators. It is found that dispersive monochromators can produce spread virtual sources of a few millimetres in size, which may prevent efficient microfocusing of the beam as required by inelastic X-ray scattering spectroscopy and other applications. Possible schemes to mitigate this problem are discussed. The analyses may provide important guidelines for designing and optimizing modern high-precision synchrotron X-ray optics and beamline instrumentation for spectroscopy, imaging and nanofocusing applications.

Inelastic X-ray scattering (IXS) is a general experimental technique for studying lattice and electronic excitations, which has undergone rapid development following the advent of the third generation synchrotron radiation facilities. X-ray Raman scattering (XRS) is inelastic scattering of X-rays due to the excitation associated with bound electrons in an atom. Its very small scattering cross-section is compensated for by a high-flux beam generated from a strong photon source. Instrumentation for IXS is now highly sophisticated, and has been applied to study a broad range of condensed matter systems [1].

This paper describes a scheme utilizing a set of low-cost and compact Kirkpatrick–Baez mirrors for upgrading the optical system of the Taiwan Inelastic X-ray Scattering beamline at SPring-8 for high-pressure experiments using diamond-anvil cells. The scheme as implemented improves the focus to 13 µm × 16 µm with transmission of up to 72%., Inelastic X-ray scattering (IXS) is a powerful technique capable of probing the dynamic behavior and electronic structure of materials. For IXS experiments under high pressure up to the megabar range using state-of-the-art diamond-anvil-cell technology, the sample volume is limited to the order of 1 × 10−3 mm3 for which a beam focus of the same order and less is often required. In this paper a scheme utilizing a set of low-cost and compact Kirkpatrick–Baez mirrors for upgrading the existing optical system of the Taiwan IXS beamline at SPring-8 is described. The scheme as implemented improves the focus to 13 µm × 16 µm (horizontal × vertical) with a transmission of up to 72% and a flux density gain of over 30 times, which has enhanced substantially the efficiency of the beamline for high-pressure research.

The THz spectrum of density fluctuations, $S(Q, \omega)$, of vitreous GeO$_2$ at ambient temperature was measured by inelastic x-ray scattering from ambient pressure up to pressures well beyond that of the known $\alpha$-quartz to rutile polyamorphic (PA) transition. We observe significant differences in the spectral shape measured below and above the PA transition, in particular, in the 30-80 meV range. Guided by first-principle lattice dynamics calculations, we interpret the changes in the phonon dispersion as the evolution from a quartz-like to a rutile-like coordination. Notably, such a crossover is accompanied by a cusp-like behavior in the pressure dependence of the elastic response of the system. Overall, the presented results highlight the complex fingerprint of PA phenomena on the high-frequency phonon dispersion., Comment: 18 pages, 5 figures

In this paper we present inelastic X-ray scattering experiments in a diamond anvil cell and molecular dynamic simulations to investigate the behavior of phononic excitations in liquid Ar. The spectra calculated using molecular dynamics were found to be in a good agreement with the experimental data. Furthermore, we observe that, upon temperature increases, a low-frequency transverse phononic gap emerges while high-frequency propagating modes become evanescent at the THz scale. The effect of strong localization of a longitudinal phononic mode in the supercritical phase is observed for the first time. The evidence for the high-frequency transverse phononic gap due to the transition from an oscillatory to a ballistic dynamic regimes of motion is presented and supported by molecular dynamics simulations. This transition takes place across the Frenkel line thermodynamic limit which demarcates compressed liquid and non-compressed fluid domains on the phase diagram and is supported by calculations within the Green-Kubo phenomenological formalism. These results are crucial to advance the development of novel terahertz thermal devices, phononic lenses, mirrors, and other THz metamaterials., 8 pages, 5 figures. arXiv admin note: text overlap with arXiv:1512.07202

We have investigated the (010) surface of $\ensuremath{\alpha}\ensuremath{-}\mathrm{Ga}$ by angle-resolved photoemission and low energy electron diffraction. We find a surface state around the $\overline{C}$ point of the surface Brillouin zone. The electron-phonon coupling at this surface is very strong with an electron-phonon mass enhancement parameter of $\ensuremath{\lambda}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1.4\ifmmode\pm\else\textpm\fi{}0.10$. Our spectra show high background intensity in a projected bulk band gap which cannot be accounted for by defect scattering and is therefore interpreted as indicating a nonquasiparticle behavior. Upon cooling the sample below 220 K we observe a phase transition accompanied by spectral changes near the Fermi level.

An X-ray Raman spectrometer for studies of local structures in minerals is discussed. Contrary to widely adopted back-scattering spectrometers using ≤10 keV X-rays, a spectrometer utilizing ~20 keV X-rays and a bent Laue analyzer is proposed. The 20 keV photons penetrate mineral samples much more deeply than 10 keV photons, so that high intensity is obtained owing to an enhancement of the scattering volume. Furthermore, a bent Laue analyzer provides a wide band-pass and a high reflectivity, leading to a much enhanced integrated intensity. A prototype spectrometer has been constructed and performance tests carried out. The oxygen K-edge in SiO(2) glass and crystal (α-quartz) has been measured with energy resolutions of 4 eV (EXAFS mode) and 1.3 eV (XANES mode). Unlike methods previously adopted, it is proposed to determine the pre-edge curve based on a theoretical Compton profile and a Monte Carlo multiple-scattering simulation before extracting EXAFS features. It is shown that the obtained EXAFS features are reproduced fairly well by a cluster model with a minimal set of fitting parameters. The spectrometer and the data processing proposed here are readily applicable to high-pressure studies.

We perform a resonant inelastic x-ray scattering (RIXS) study of Ni-substituted La{sub 2}CuO{sub 4} and Cu-substituted La{sub 2}NiO{sub 4}. Resonantly enhanced charge-transfer excitations are successfully observed by tuning the incident photon energy to the K edge of the substituted element. These excitations display a very weak momentum dependence, evidencing their local character. We find a shift in the energy of the onset edge of these features compared with the nonsubstituted compounds La{sub 2}CuO{sub 4} and La{sub 2}NiO{sub 4}. This shift is quantitatively reproduced by exact diagonalization calculations of the RIXS spectra. RIXS is shown to be a powerful tool to probe the electronic states of substituted elements and to understand their interaction with surrounding atoms.

We have successfully determined the hitherto unknown sign of the ${B}_{4}^{4}$ Stevens crystal-field parameter of the tetragonal heavy-fermion compound ${\mathrm{CeCu}}_{2}{\mathrm{Si}}_{2}$ using vector $\stackrel{^}{\mathbf{q}}$-dependent nonresonant inelastic x-ray scattering experiments at the cerium ${N}_{4,5}$ edge. The observed difference between the two different directions, $\stackrel{^}{\mathbf{q}}\ensuremath{\parallel}[100]$ and $\stackrel{^}{\mathbf{q}}\ensuremath{\parallel}[110]$, is due to the anisotropy of the crystal-field ground state in the (001) plane and is observable only because of the utilization of higher than dipole transitions possible in nonresonant inelastic x-ray scattering. This approach allows us to go beyond the specific limitations of dc magnetic susceptibility, inelastic neutron scattering, and soft x-ray spectroscopy, and provides us with a reliable information about the orbital state of the $4f$ electrons relevant for the quantitative modeling of the quasiparticles and their interactions in heavy-fermion systems.

Theoretical analysis of high-energy-resolution x-ray optics, such as backscattering 1-3 and four-bounce 4-5 monochromators and analyzers, has been carried out using computer modeling within the framework of the dynamical theory of x-ray diffraction. This analysis identifies several important techniques for the precise alignment and determination of the energy and bandwidth of the monochromat ors. The destructive contribution of mu ltiple-wave diffraction to the scattering intensity of x-ray backscattering optics has also been analyzed in details. An important method has been identified which allows this destructive contribution to be avoided. Keywords: x-ray optics, x-ray diffraction, high-energy-resolution, monochromators, analyzers, computer modeling 1. INTRODUCTION In the last decade an increasing effort has been focused to the upgrade of Inelastic X Ra y Scattering (IXS) spectrometers, aiming at improving both resolution bandwidth and spectral contrast 1 . In the long run, the ultimate objective of this activity is to bridge the dynamic gap which presently separates IXS from low energy and low momentum transfer spectroscopic techniques. The access to such spectroscopic region will allow the investigation of a wealth of still unexplored physical phenomena as diverse as slow relaxations in highly viscous materials such as glass formers, colloids and polymers, nanoscale arrangements of molecular clusters or confined liquids, and collective modes propagating through lipid membranes, etc. For achieving this objective, new concept optical schemes based on the dispersive nature of Bragg back-reflection from asymmetrically cut crystals promise to open up new avenues

The THz dynamics of liquid glycerol has been probed by inelastic x-ray scattering at different pressure spanning the 0.66–3 Kbar range. A comparison with ultrasound absorption results available in literature leads us to identify the presence of two different relaxations, a structural (slow) relaxation and a microscopic (fast) one. Although the former has been already thoroughly studied in glycerol by lower frequency spectroscopic techniques, no hints on the latter are so far available in literature. We observe that the characteristic timescale of this fast relaxation ranges in the sub-picosecond, tends to decrease with increasing the wave-vector and seems rather insensitive to pressure changes. Finally, the timescale and strength of the fast relaxation have a direct link revealing the microscopic, single particle, nature of the involved process.

The state-resolved differential cross sections for both the $1{s}^{2}$ ${}^{1}{S}_{0}\ensuremath{\rightarrow}1s2s$ ${}^{1}{S}_{0}$ monopolar transition and the $1{s}^{2}$ ${}^{1}{S}_{0}\ensuremath{\rightarrow}1s2p$ ${}^{1}{P}_{1}$ dipolar transition of atomic helium had been measured over a large momentum transfer region by high-resolution inelastic x-ray scattering (IXS). The almost-perfect match of the present measurement with the theoretical calculations gives a stringent test of the theoretical method and the calculated wave functions. Our results demonstrate that high-resolution IXS is a powerful tool for studying the excitations in atoms and molecules.

Using inelastic x-ray scattering techniques, we have succeeded in probing the high-pressure electronic structure of helium at 300 K. Helium has the widest known valence-conduction band gap of all materials a property whose high-pressure response has been inaccessible to direct measurements. We observed a rich electron excitation spectrum, including a cutoff edge above 23 eV, a sharp exciton peak showing linear volume dependence, and a series of excitations and continuum at 26 to 45 eV. We determined the electronic dispersion along the Γ-M direction over two Brillouin zones, and provided a quantitative picture of the helium exciton beyond the simplified Wannier-Frenkel description.

International audience; The electron energy-loss function of graphite is studied for momentum transfers q beyond the first Brillouin zone. We find that near Bragg reflections the spectra can change drastically for very small variations in q. The effect is investigated by means of first principle calculations in the random phase approximation and confirmed by inelastic x-ray scattering measurements of the dynamic structure factor S(q,ω). We demonstrate that this effect is governed by crystal local field effects and the stacking of graphite. It is traced back to a strong coupling between excitations at small and large momentum transfers.

One of the major goals of the National Synchrotron Light Source II project is to achieve ultrahigh energy resolution up to 0.1 meV for medium-energy inelastic X-ray scattering spectroscopy based on the angular dispersion optics employing extremely asymmetric backscattering geometry. In this papaer, we describe the complete monochromatization mechanisms underlying the new optics. We have also designed and tested a CDW-CDW prototype under ambient condition, with which we have successfully demonstrated the important angular dispersion effect, the Borrman enhanced transmission effect, and other optical principles involved in every step of the entire diffraction process, and found good agreement with the theoretical expectations. These studies indicate that the new optics are feasible in principle but face some technical challenges that need to be solved by our future systematic research and development activities before their practical applications.

The pressure-induced valence transition in TmTe was investigated by resonant inelastic x-ray scattering at the Tm ${L}_{3}$ edge, a powerful probe of the rare-earth valent state. The data are analyzed within the Anderson impurity model which yields key parameters such as the Tm $4f\ensuremath{-}5d$ hybridization. In addition to the general tendency of the $f$ electrons towards delocalization, we find a plateau in both the Tm valence and hybridization pressure dependences between 4.3 and 6.5 GPa which is interpreted in terms of an $n$-channel Kondo (NCK) screening process. This behavior is at odds with the usually continuous, single-channel Kondo-like $f$ delocalization while being supported by the seminal calculations of the NCK temperature in Tm ion by Saso et al. Our study raises the interesting possibility that an NCK effect realized in a compressed mixed-valent $f$ system could impede the concomitant electron delocalization.

A sharp feature in the charge-density excitation spectra of single-crystal MgB2, displaying a remarkable cosinelike, periodic energy dispersion with momentum transfer (q) along the c* axis, has been observed for the first time by high-resolution nonresonant inelastic x-ray scattering (NIXS). Time-dependent density-functional theory calculations show that the physics underlying the NIXS data is strong coupling between single-particle and collective degrees of freedom, mediated by large crystal local-field effects. As a result, the small-q collective mode residing in the single-particle excitation gap of the B pi bands reappears periodically in higher Brillouin zones. The NIXS data thus embody a novel signature of the layered electronic structure of MgB2.

In this work we investigate the relevance of phonons for the superconductivity in Na0.35CoO2 · 1.3H2O. We measure phonon dispersion in this material as well as in the nonhydrated parent compound Na0.7CoO2 by inelastic x-ray scattering. The measured phonon dispersion along the

The dynamics of doped charge in an antiferromagnetic lattice is central to the description of the insulator-metal transition that occurs on doping the parent high Tc compounds. In this work we use high resolution resonant inelastic x-ray scattering to investigate the dynamics of the charge-transfer exciton by measuring its energy dispersion in two prototype compounds, La2 CuO4 and La2 NiO4 . We show that this behavior is radically different in the cuprate with respect to a system known to exhibit strong polaronic behavior, namely, the nickelate: the exciton is mobile in the cuprate while it is well localized in the nickelate. Using a simple Wannier-Mott model we can estimate the total hole plus electron effective mass in the cuprate to be 3:5

Excitons in a complex organic molecular crystal were studied by inelastic x-ray scattering (IXS) for the first time. The dynamic dielectric response function is measured over a large momentum transfer region, from which an exciton dispersion of 130 meV is observed. Semiempirical quantum chemical calculations reproduce well the momentum dependence of the measured dynamic dielectric responses, and thus unambiguously indicate that the lowest Frenkel exciton is confined within a fraction of the complex molecule. Our results demonstrate that IXS is a powerful tool for studying excitons in complex organic molecular systems. Besides the energy position, the IXS spectra provide a stringent test on the validity of the theoretically calculated exciton wave functions., 4 pages, 4 figures

The electronic structure of thulium monochalcogenides $\mathrm{Tm}X$ $(X=\mathrm{S},\mathrm{Se},\mathrm{Te})$ is investigated by x-ray absorption spectroscopy (XAS) in the partial fluorescence yield mode (PFY-XAS) and resonant x-ray emission spectroscopy around and far below the edge. These three resonant inelastic x-ray scattering (RIXS)-derived techniques yield consistent values of the thulium valency of 2.67, 2.65, and 2.70, respectively, in the mixed-valent compound TmSe. These values are in closer agreement with the valency derived from the lattice parameter measurement compared to previous x-ray photoemission spectroscopy and XAS studies. The study demonstrates that RIXS is a powerful and accurate probe of mixed-valent states in $f$-electron systems.

The near K-edge structure of oxygen in liquid water and ices III, II, and IX at 0.25 GPa and several low temperatures down to 4 K has been studied using inelastic x-ray scattering at 9884.7 eV with a total energy resolution of 305 and 175 meV. A marked decrease of the preedge intensity from the liquid phase and ice III to ices II and IX is attributed to ordering of the hydrogen bonds in the proton-ordered lattice of the latter phases. Density functional theory calculations including the influence of the Madelung potential of the ice IX crystal correctly account for the remaining preedge feature. Furthermore, we obtain spectroscopic evidence suggesting a possible new phase of ice at temperatures between 4 and 50 K.

Crystal analyzers produced by spherically bending a Si crystal wafer are employed in high‐resolution inelastic x‐ray scattering experiments to increase the counting efficiency. The fabrication commonly involves dicing the crystal wafer into blocks of ∼1mm×1mm to release the bending strain before gluing the wafer onto a spherical substrate. During the gluing, the relative alignment of each block must be maintained to achieve the desired focusing effect. A novel pressing tool has been designed to apply uniform pressure on the wafer during the gluing process to ensure the relative alignment between the crystal blocks, and has produced analyzers with satisfactory performance. The design details and the fabrication process will be presented and discussed.

The ultrahigh resolution IXS beamline of NSLS-II is designed to probe a region of dynamic response that requires an ultrahigh energy and momentum resolution of up to 0.1 meV and < 0.1 nm -1 , respectively, which is currently still beyond the reach of existing low and high frequency inelastic scattering probes. Recent advances at NSLS-II in developing the required x-ray optics and instrumentation based on the use of extremely asymmetric Bragg back reflections of Si have allowed us to achieve sub-meV energy resolution with sharp tails and high efficiency at a medium energy of around 9.1 keV, thereby validating the optical design of the beamline for the baseline scope and paving the way for further development towards the ultimate goal of 0.1 meV. The IXS beamline is expected to provide a broad range of scientific opportunities, particularly in areas of liquid, disordered and bio-molecular systems.

For the past few years, silicon (800) asymmetric back-diffraction at 9.13 keV has been investigated for use in inelastic x-ray scattering (IXS) analyzer with 100 μrad acceptance. While the basic principles have been described and proven, attractive results have become consistently achievable only recently, with particular attention paid to key execution details, including crystal quality (substrate purity, orientation, surface flatness and strain), positioning (resolution, repeatability, and stability of critical axes), thermal environment stability and control, and x-ray diagnostics. While methods for positioning, diagnostics, and thermal stabilization have been refined in our work, crystal quality remains a critical limitation of ultimate performance. An overview of the implementation details is provided in the context of prototype x-ray beam test results collected in preparation for final design of the analyzer instrument to be incorporated into the IXS beamline of NSLS-II.

Charge-transfer excitation is at the source of the photoinduced magnetism observed in several Prussian blue molecule-based magnets. Using resonant inelastic x-ray scattering and x-ray absorption spectroscopy, we probe directly the thermally activated charge transfer in a photomagnetic Fe-Co cyanide, Cs0.7Co4[Fe(CN)6]2.9[◻]1.1.16H2O, where [◻] represents [Fe(CN)6] vacancies. The temperature dependence of both Co and Fe valence ratios is estimated for the first time in one cooling run, thus yielding a more complete picture of the temperature-induced cooperative electronic modifications. This novel approach, benefiting from relatively short acquisition times, opens the possibility for realtime characterization of the photoinduced magnetism in molecule-based magnets.