György Vankó

• PhD
• Group Leader at Hungarian Academy of Sciences

We report X-ray emission spectra of Fe(III), Fe(II), and Co(II) spin-crossover compounds in their high-spin and low-spin forms. It is shown that all X-ray emission features are sensitive to the spin state. Variations of the Kbeta and the Kalpha emission line shapes, which are in agreement with theory, can be used as quantitative probes of the spin...

(Figure Presented) Ultrafast spin probe: A short-lived transient species of light-excited [Fe(bpy)3]2+ (bpy = 2,2′-bipyridine) shows geometry variations that correspond to excitation to a high-spin state, in which the spin momentum of Fe" has now been directly determined to be S = 2 by spin-sensitive ultrafast X-ray emission spectroscopy.

Theoretical predictions show that depending on the populations of the Fe 3d xy , 3d xz , and 3d yz orbitals two possible quintet states can exist for the high-spin state of the photoswitchable model system [Fe(terpy)2]2+. The differences in the structure and molecular properties of these 5B2 and 5E quintets are very small and pose a substantial...

High energy resolution, hard X-ray spectroscopies are powerful element selective probes of the electronic and local structure of matter, with diverse applications in chemistry, physics, biology and materials science. The routine application of these techniques is hindered by the complicated and slow access to synchrotron radiation facilities. Here...

Substitution of terpyridine at the 4’ position with electron withdrawing and donating groups is used to tune the quintet lifetime of the iron(II) complex. DFT calculations suggest that the energy barrier between the quintet and singlet states can be altered significantly upon substitution, inducing a large variation of the lifetime of the photoexci...

[Fe(terpy)2]2+ (terpy = 2,2′:6′,2″-terpyridine) is a transition metal complex where the spin state is photoswitchable and where the properties of the metal-centered quintet excited state (⁵MC) can be tuned by substituting different electron withdrawing or electron donating groups on the 4′ position of the terpyridine. To better understand the physi...

[Fe(terpy)2]2+ (terpy = 2,2':6',2''-terpyridine) is a transition metal complex where the spin state is photoswitchable and where the properties of the metal-centered quintet excited state (5MC) can be tuned by substituting different Electron Withdrawing (EW) or Electron Donating (ED) groups on the 4' position of the terpyridine. To better understan...

We previously studied the effect of 4' substitution in iron(II)-bis-terpyridine complexes, showing that the photoexcited high-spin quintet-state is stabilized by electron-donating substituents. In this paper we explore the effects of electron-donating ( X = NH2 , Cl ) and withdrawing ( X = NO2 ) substituents in the 5,5" positions on the stability a...

The application of N -heterocyclic carbene (NHC) ligands represents a groundbreaking advance towards environment-friendly light-harvesting complexes, yet, even the excited-state dynamics of the first-discovered Fe-NHC photosensitiser [Fe(bmip) 2 ] ²⁺ (bmip = 2,6-bis(3-methyl-imidazole-1-ylidine)-pyridine) remain...

The application of N-heterocyclic carbene (NHC) ligands represents a groundbreaking advance towards environment-friendly light-harvesting complexes, yet, even the excited-state dynamics of the first-discovered Fe-NHC photosensitiser [Fe(bmip)2]2+ (bmip = 2,6-bis(3-methyl-imidazole-1-ylidine)-pyridine) remain controversial. Using full-dimensional tr...

The properties of transition-metal complexes and their chemical dynamics can be effectively modified with ligand substitutions, and theory can be a great aid to such molecular engineering. In this paper, we first theoretically explored how substitution with a Cl atom at different positions of the terpyridine ligand affects the electronic structure...

Photochemical reactions in solution are governed by a complex interplay between transient intramolecular electronic and nuclear structural changes and accompanying solvent rearrangements. State-of-the-art time-resolved X-ray solution scattering has emerged in the last decade as a powerful technique to observe solute and solvent motions in real time...

It has long been known that irradiation with visible light converts Fe(II) polypyridines from their low-spin (singlet) to high-spin (quintet) state, yet mechanistic interpretation of the photorelaxation remains controversial. Herein, we simulate the full singlet-triplet-quintet dynamics of the [Fe(terpy)2]²⁺ (terpy = 2,2’:6’,2”-terpyridine) complex...

The properties of transition metal complexes and their chemical dynamics can be effectively modified with ligand substitutions, and theory can be a great aid to such molecular engineering. In this paper we first theoretically explore how substitution with a Cl atom at different positions of the terpyridine ligand affects the electronic structure of...

Photochemical reactions in solution are governed by a complex interplay between transient intramolecular electronic and nuclear structural changes and accompanying solvent rearrangements. State-of-the-art time-resolved X-ray solution scattering has emerged in the last decade as a powerful technique to observe solute and solvent motions in real time...

We present a sub-picosecond resolved investigation of the structural solvent reorga-nization and geminate recombination dynamics following 400 nm two-photon exci-tation and photodetachment of a valence p electron from the aqueous atomic so-lute, I ⁻ (aq). The measurements utilized time-resolved X-ray Absorption Near EdgeStructure (TR-XANES) spectro...

It has long been known that irradiation with visible light converts Fe(II) polypyridines from their low-spin (singlet) to high-spin (quintet) state, yet mechanistic interpreation of the photorelaxation remains contraversal. Herein, we simulate the full singlet-triplet-quintet dynamics of the [Fe(terpy)2]2+ (terpy = 2,2’:6’,2’’-terpyridine) complex...

The present work demonstrates the performance of a von Hámos high-energy-resolution X-ray spectrometer based on a non-conventional conical Si single-crystal analyzer. The analyzer is tested with different primary and secondary X-ray sources as well as a hard X-ray sensitive CCD camera. The spectrometer setup is also characterized with ray-tracing s...

Time‐resolved X‐ray absorption spectroscopy has been utilized to monitor the bimolecular electron transfer in a photocatalytic water splitting system. This has been possible by uniting the local probe and element specific character of X‐ray transitions with insights from high‐level ab initio calculations. The specific target has been a heteroleptic...

DOI:https://doi.org/10.1103/PhysRevLett.124.199902

The non-equilibrium dynamics of electrons and nuclei govern the function of photoactive materials. Disentangling these dynamics remains a critical goal for understanding photoactive materials. Here we investigate the photoinduced dynamics of the [Fe(bmip)2]²⁺ photosensitizer, where bmip = 2,6-bis(3-methyl-imidazole-1-ylidine)-pyridine, with simulta...

Femtosecond electronic and nuclear dynamics in [Cu(dmp) 2 ] ⁺ complex upon 550 nm photoexcitation are studied with X-ray emission spectroscopy and X-ray solution scattering, revealing pseudo Jahn-Teller distortion (~410 fs) coupled with coherent vibrational motion.

Time-resolved X-ray absorption spectroscopy has been utilized to monitor the bimolecular electron transfer in a photocatalytic water splitting system for the first time. This has been possible by uniting the local probe and element specific character of X-ray transitions with insights from high-level ab initio calculations. The specific target has...

Iron N‐heterocyclic carbene (NHC) complexes have received a great deal of attention recently because of their growing potential as light sensitizers or photocatalysts. We present a sub‐ps X‐ray spectroscopy study of an FeIINHC complex that identifies and quantifies the states involved in the deactivation cascade after light absorption. Excited mole...

Disentangling the dynamics of electrons and nuclei during nonadiabatic molecular transformations remains a considerable experimental challenge. Here we have investigated photoinduced electron transfer dynamics following a metal-to-ligand charge-transfer (MLCT) excitation of the [Fe(bmip)2]2+ photosensitizer, where bmip = 2,6-bis(3-methyl-imidazole-...

Ligand substitution reactions are common in solvated transition metal complexes, and harnessing them through initiation with light promises interesting practical applications, driving interest in new means of probing their mechanisms. Using a combination of time-resolved x-ray absorption spectroscopy and hybrid quantum mechanics/molecular mechanics...

Iron nitrogen heterocyclic carbenes (NHC) have received a great deal of attention recently, due to their growing potential as e.g light sensitizers and photocatalysts. We present a sub‐ps x‐ray spectroscopy study of a FeIINHC complex allowing us to identify and quantify the states involved in the deactivation cascade after light absorption. We find...

Disentangling the strong interplay between electronic and nuclear degrees of freedom is essential to achieve a full understanding of excited state processes during ultrafast nonadiabatic chemical reactions. However, the complexity of multi-dimensional potential energy surfaces means that this remains challenging. The energy flow during vibrational...

We have employed a range of ultrafast X-ray spectroscopies in an effort to characterize the lowest energy excited state of [Fe(dcpp)2]2+ (where dcpp is 2,6-(dicarboxypyridyl)pyridine). This compound exhibits an unusually short excited-state lifetime for a low-spin Fe(II) polypyridyl complex of 270 ps in a room-temperature fluid solution, raising qu...

Light-driven molecular reactions are dictated by the excited state potential energy landscape, depending critically on the location of conical intersections and intersystem crossing points between potential surfaces where non-adiabatic effects govern transition probabilities between distinct electronic states. While ultrafast studies have provided...

Aqueous solutions of the ternary system Ni(II)-EDTA-CN- are investigated with X-ray Absorption Spectroscopy (XAS) as a function of cyanide concentration with an enhanced laboratory von Hámos X-ray spectrometer. The near-edge structure of the spectra identifies unambiguously the formation of the pentacyanidonickel(II) complex at excess CN- concentra...

Basic principles and recent work using probes including Mössbauer, optical, X-ray, and vibrational spectroscopies to follow the transitions in spin crossover complexes are reviewed. X-ray spectroscopy, being a relatively lesser-known probe, is discussed in more detail. X-ray spectroscopic methods have been used in the spin crossover field mostly to...

X-ray emission and x-ray Raman scattering spectroscopy are powerful tools to investigate the local electronic and atomic structure of high and low Z elements in-situ. Notably, these methods can be applied for in-situ spectroscopy at high pressure and high temperature using resistively or laser-heated diamond anvil cells in order to achieve thermody...

The excited state dynamics of solvated [Fe(bpy)(CN)4]2-, where bpy = 2,2’-bipyridine, show significant sensitivity to the solvent Lewis acidity. Using a combination of optical absorption and X-ray emission transient spectroscopies, we have previously shown that the metal to ligand charge transfer (MLCT) excited state of [Fe(bpy)(CN)4]2- has a 19 pi...

The structural variations and stability constants of the forming complexes were determined in the Ni−EDTA−CN⁻ (EDTA = ethylenediaminetetraacetic acid) ternary system from a single laboratory X-ray absorption near-edge structure measurement series with our recently developed von Hámos type high-resolution laboratory X-ray spectrometer, demonstrating...

We probe the dynamics of valence electrons in photoexcited [Fe(terpy)2]²⁺ in solution to gain deeper insight in the Fe-ligand bond changes. We use hard X-ray emission spectroscopy (XES), which combines element specificity and high penetration with sensitivity to orbital structure, making it a powerful technique for molecular studies in a wide varie...

Ultrafast pump-probe spectroscopy within the X-ray regime is now possible owing to the development of X-ray Free Electrons Lasers (X-FELs) and is opening new opportunities for the direct probing of femtosecond evolution of the nuclei, the electronic and spin degrees of freedom. In this contribution we use wavepacket dynamics of the photoexcited dec...

High energy resolution, hard X-ray spectroscopies are powerful element selective probes of the electronic and local structure of matter, with diverse applications in chemistry, physics, biology and materials science. The routine application of these techniques is hindered by the complicated and slow access to synchrotron radiation facilities. Here...

We study the structural dynamics of photoexcited [Co(terpy)2]2+ in an aqueous solution with ultrafast x-ray diffuse scattering experiments conducted at the Linac Coherent Light Source. Through direct comparisons with density functional theory calculations, our analysis shows that the photoexcitation event leads to elongation of the Co-N bonds, foll...

We study the structural dynamics of photoexcited [Co(terpy)2]2+ in an aqueous solution with ultrafast x-ray diffuse scattering experiments conducted at the Linac Coherent Light Source. Through direct comparisons with density functional theory calculations, our analysis shows that the photoexcitation event leads to elongation of the Co-N bonds, foll...

Fe(II) complexes have long been assumed unsuitable as photosensitisers because of their low-lying non-emissive metal centred (MC) states, which inhibit electron transfer. Herein, we describe the excited state relaxation of a novel Fe(II) complex that incorporates N-heterocyclic carbene ligands designed to destabilise the MC states. Using first prin...

In liquid phase chemistry dynamic solute-solvent interactions often govern the path, ultimate outcome and efficiency of chemical reactions. These steps involve many-body movements on sub-picosecond (ps) time scales, and thus ultrafast structural tools capable of capturing both intramolecular electronic and structural changes and local solvent struc...

Ultrafast X-ray techniques serve as a direct probe of a long-lived pseudo-octahedral high-valent iron(V) complex. Its photo-induced formation from an azido-iron(III) precursor is observed in real-time with sub-picosecond resolution at SACLA XFEL.

Ultrafast photoinduced electron transfer preceding energy equilibration still poses many experimental and conceptual challenges to the optimization of photoconversion since an atomic-scale description has so far been beyond reach. Here we combine femtosecond transient optical absorption spectroscopy with ultrafast X-ray emission spectroscopy and di...

X-ray spectroscopies, when combined in laser-pump, X-ray-probe measurement schemes, can be powerful tools for tracking the electronic and geometric structural changes that occur during the course of a photoinitiated chemical reaction. X-ray absorption spectroscopy (XAS) is considered an established technique for such measurements, and X-ray emissio...

We have studied the photoinduced low spin (LS) to high spin (HS) conversion of aqueous Fe(bpy)3 with pulse-limited time resolution. In a combined setup permitting simultaneous X-ray diffuse scattering (XDS) and spectroscopic measurements at a MHz repetition rate we have unraveled the interplay between intramolecular dynamics and the intermolecular...

Earth-abundant transition-metal complexes are desirable for sensitizers in dye-sensitized solar cells or photocatalysts. Iron is an obvious choice, but the energy level structure of its typical polypyridyl complexes, featuring low-lying metal-centered states, has made such complexes useless as energy converters. Recently, we synthesized a novel iro...

Crucial to many light-driven processes in transition metal complexes is the absorption and dissipation of energy by 3d electrons. But a detailed understanding of such non-equilibrium excited-state dynamics and their interplay with structural changes is challenging: a multitude of excited states and possible transitions result in phenomena too compl...

The performance of six frequently used density functional theory (DFT) methods (RPBE, OLYP, TPSS, B3LYP, B3LYP*, and TPSSh) in the prediction of Mössbauer isomer shifts(δ) and quadrupole splittings (ΔEQ) is studied for an extended and diverse set of Fe complexes. In addition to the influence of the applied density functional and the type of the bas...

The nanoscopic magneto-electronic phase separation in doped La1-xSrxCoO3 perovskites was studied with local probes. The phase separation is directly observed by M\"ossbauer spectroscopy in the studied doping range of 0.05 <= x <= 0.25 both at room-temperature as well as in the low temperature magnetic phase. Extended with current synchrotron based...

Building a detailed understanding of the structure function relationship is a crucial step in the optimization of molecular photocatalysts employed in water splitting schemes. The optically dark nature of their active sites usually prevents a complete mapping of the photoinduced dynamics. In this work, transient X-ray absorption spectroscopy highli...

We report on extending hard X-ray emission spectroscopy (XES) along with resonant inelastic X-ray scattering (RIXS) to study ultrafast phenomena in a pump-probe scheme at MHz repetition rates. The investigated systems include low-spin (LS) FeII complex compounds, where optical pulses induce a spin-state transition to their (sub)nanosecond-lived hig...

The sensitivity of the 1s X-ray emission and high-energy-resolution fluorescence-detected X-ray absorption spectroscopies (XES and HERFD-XAS) to resolve the variations in the chemical state (electronic structure and local coordination) of Br has been investigated for a selected set of compounds including NaBrO3, NH4Br and C2H4Br2 (1,2-dibromoethane...

The temperature-dependent 1s2p resonant inelastic X-ray scattering (RIXS) spectra of CoO have been measured with 0.3 eV overall resolution, and the RIXS planes have been analyzed with multiplet calculations. The analysis of the high-resolution 1s2p RIXS plane allows a more detailed determination of the ground-state electronic structure, as compared...

The electronic structure relevant to low spin (LS)↔high spin (HS) transitions in Fe(II) coordination compounds with a FeN6 core are studied. The selected [Fe(tz)6]2+ (1) (tz = 1H-tetrazole), [Fe(bipy)3]2+ (2) (bipy = 2,2′-bipyridine), and [Fe(terpy)2]2+ (3) (terpy = 2,2′:6′,2″-terpyridine) complexes have been actively studied experimentally, and wi...

Reciprocity is when the scattering amplitude of wave propagation satisfies a symmetry property, connecting a scattering process with an appropriate reversed one. We report on an experiment using nuclear resonance scattering of synchrotron radiation, which demonstrates that magneto-optical materials do not necessarily violate reciprocity. The settin...

We have studied the photoinduced low spin (LS) to high spin (HS) conversion of [Fe(bipy)(3)](2+) in aqueous solution. In a laser pump/X-ray probe synchrotron setup permitting simultaneous, time-resolved X-ray diffuse scattering (XDS) and X-ray spectroscopic measurements at a 3.26 MHz repetition rate, we observed the interplay between intramolecular...

In this contribution, we report the first hard-X-ray-induced thermal hysteresis (HAXITH). The bistability in [Fe(phen)2(SCN)2] (phen = 1,10-phenanthroline) is proven by alternately heating and cooling the sample under permanent irradiation with hard X-rays. Within the hysteresis a serpentine-like switching effect is observed. HAXITH is a new tool t...

We have measured plasmon energies in Na under high pressure up to 43 GPa using inelastic x-ray scattering (IXS). The momentum-resolved results show clear deviations, growing with increasing pressure, from the predictions for a nearly free-electron metal. Plasmon energy calculations based on first-principles electronic band structures and a quasicla...

We have measured plasmon energies in Na under high pressure up to 43 GPa using inelastic x-ray scattering (IXS). The momentum-resolved results show clear deviations, growing with increasing pressure, from the predictions for a nearly-free electron metal. Plasmon energy calculations based on first-principles electronic band structures and a quasi-cl...

We present experimental inelastic x-ray scattering (IXS) and ab initio time-dependent density-functional-theory (TDDFT) studies of YBa2Cu3O7−δ. The response of the low-lying Ba 5p and Y 4p core electrons is shown to interact strongly with the Cu 3d and O 2p excitations, with important consequences on screening. The agreement between IXS and TDDFT r...

We present experimental inelastic x-ray scattering (IXS) and ab initio time-dependent density-functional-theory (TDDFT) studies of YBa2Cu3O7-delta . The response of the low-lying Ba5p and Y4p core electrons is shown to interact strongly with the Cu3d and O2p excitations, with important consequences on screening. The agreement between IXS and TDDFT...

Contribution to a conf. proceeding (journal)

Angular dependent core-hole screening effects have been found in the cobalt K-edge x-ray absorption spectrum of LiCoO2, using high-resolution data and parameter-free GGA+U calculations. The Co 1s core-hole on the absorber causes strong local attraction. The core-hole screening on the nearest neighbours cobalt induces a 2 eV shift in the density of...

A multiple-analyser-crystal spectrometer for non-resonant inelastic X-ray scattering spectroscopy installed at beamline ID16 of the European Synchrotron Radiation Facility is presented. Nine analyser crystals with bending radii R = 1 m measure spectra for five different momentum transfer values simultaneously. Using a two-dimensional detector, the...

We develop a general procedure to analyse the pre-edges in 1s x-ray absorption near edge structure (XANES) of transition metal oxides and coordination complexes. Transition metal coordination complexes can be described from a local model with one metal ion. The 1s 3d quadrupole transitions are calculated with the charge-transfer multiplet program....

Silicate post-perovskite and perovskite are believed to be the dominant minerals of the lowermost mantle and the lower mantle, respectively, and their properties, which can be strongly influenced by the electronic state of iron in these phases, affect our understanding of the nature of the deep Earth. To date, in these minerals the electronic spin...

The core and valence levels of β-PbO2 have been studied using hard X-ray photoemission spectroscopy (hν = 6000 eV and 7700 eV). The Pb 4f core levels display an asymmetric lineshape which may be fitted with components associated with screened and unscreened final states. It is found that intrinsic final state screening is suppressed in the near-sur...

Iron-bearing silicate post-perovskite and perovskite are believed to be the dominant minerals of the lowermost mantle and the lower mantle, respectively. The electronic spin state of iron—a quantum property of every electron associated with its angular momentum—can strongly influence the properties of these mineral phases and thereby the nature of...

Charge-neutral dd excitations in NiO have been studied using resonant inelastic x-ray scattering (RIXS) at the quadrupolar pre-edge of the Ni K absorption edge (8331 eV) with an energy resolution of 250 meV. The results agree well with calculations performed using the atomic multiplet model for the Ni2+ ion including crystal-field effects. Most not...

A Reply to the Comment by Alexander J. M. Schmets and Wouter Montfrooij.

The pre-edge structure of Cu1s excitations of high Tc cuprates reflects the lowest-lying unoccupied electronic states in these materials, and thus it is directly relevant to the interesting low-energy excitations and their nonlocal characters. We have performed theoretical calculations of the CuKalpha resonant x-ray emission spectroscopy (RXES) in...

Oxygen K-edge x-ray absorption spectra of high-density amorphous (HDA) ice, low-density amorphous ice Ic, ice Ih, normal and deuterated liquid water were measured with the synchrotron x-ray Raman scattering method under almost identical experimental conditions by in situ heating of an HDA ice sample. The distinct preedge structure previously report...

We report core level and valence band photoemission results obtained for Nd2−xCexCuO4 (x=0.15) single crystals and films by using both soft and hard x rays, hence, with tunable depth sensitivity. When using hard x rays only, we observe distinct and energy separated structures in the main 2p53d9L peak of Cu 2p3/2 and 2p1/2 core levels, including the...

We report on strong dipole transitions to 3d orbitals of neighboring Co atoms in the Co 1s x-ray absorption pre-edge. They are revealed by applying high-resolution resonant x-ray emission spectroscopy (RXES) to compounds containing CoO6 clusters. When contrasted to quadrupole local 1s3d excitations, these non-local 1s3d transitions are identified b...

Inelastic x-ray scattering has been utilized to study the elementary excitations of normal liquid 3He at the temperature T=1.10+/-0.05 K and saturated vapor pressure in the wave vector range 0.15<or=Q<or=3.15 A(-10. The present data provide direct information on the zero-sound mode in the mesoscopic wave vector range where it was expected to decay...

Mineral properties in Earth's lower mantle are affected by iron electronic states, but representative pressures and temperatures have not yet been probed. Spin states of iron in lower-mantle ferropericlase have been measured up to 95 gigapascals and 2000 kelvin with x-ray emission in a laser-heated diamond cell. A gradual spin transition of iron oc...

We have investigated the magnetic state of iron in siderite FeCO3 under high pressure using Kβ x-ray emission spectroscopy. Pressure induced changes in the shape of the iron Kβ emission lines indicate that the iron ground state changes from a low pressure magnetic state to a high pressure non-magnetic state. This transition takes place roughly at 5...

We have measured the uranium L3 absorption and resonant emission spectra in the localized magnetic compound UPd3 and heavy fermion UPd2Al3 as a function of pressure. The spectral line shape of the absorption edge is found to vary rapidly in UPd2Al3 with a notable broadening of the white line above the structural transition around 25 GPa while it sh...

Zwei Wege, ein Ziel: Harte Röntgenstrahlen können bei tiefer Temperatur lichtschaltbare molekulare Spinübergangsverbindungen in metastabile High-Spin-Zustände anregen (siehe Bild). Diese haben ähnliche spektroskopische Eigenschaften wie die bekannten LIESST-Zustände, und die Bildungs- und Zerfallsreaktionen deuten auf ähnliche Mechanismen hin. Dami...

All Xcited: At low temperatures, an intense beam of hard X-rays excites photoswitchable molecular spin-crossover systems to generate metastable high-spin states (see picture). These states have spectroscopic properties similar to those of the states generated by light-induced excited-spin-state trapping. The new approach offers an excitation source...

The giant dipole resonance of Ba embedded into the complex Si host lattice structure of Ba8Si46 has been observed under ambient and high-pressure conditions. The measurements have been accomplished using nonresonant inelastic x-ray scattering for different momentum transfers. The resonance appears as a broad feature between 100- and 150-eV energy l...

We investigate the magnetic properties of archetypal transition-metal oxides MnO, FeO, CoO, and NiO under very high pressure by x-ray emission spectroscopy at the Kbeta line. We observe a strong modification of the magnetism in the megabar range in all the samples except NiO. The results are analyzed within a multiplet approach including charge-tra...

In a recent paper, Kantor presented Mossbauer spectroscopy data on the pressure dependence of the Fe spin state in Mg1-xFexO [Phys. Rev. B 73, 100101(R) (2006)] and found that the transition was completed at significantly higher pressures than what had been found by x-ray emission spectroscopy (XES) studies. In order to account for the discrepancy,...

Using Co Kβ x-ray emission spectroscopy (XES) we have investigated the effect of pressure on the Co spin state of a single crystal of metallic, ferromagnetic La0.82Sr0.18CoO3. The analysis of the XES spectra up to 14.4 GPa at 300 and 34 K clearly shows a gradual pressure-induced spin-state transition from a high- or intermediate-spin to a low-spin...

The nature of electronic states at the Fermi energy in metallic β-PbO2 has been identified by hard x-ray photoemission spectroscopy (HXPS) combined with x-ray emission spectroscopy and density-functional theory calculations. Pb 6s states are strongly enhanced in HXP spectra, allowing us to locate the Fermi level above the top of the valence band. T...

Pressure-induced electronic spin-pairing transitions of iron and associated effects on the physical properties have been reported to occur in the lower-mantle ferropericlase, silicate perosvkite, and perhaps in post silicate perovskite at high pressures and room temperature. These recent results are motivating geophysicists and geodynamicists to re...

We exploited complementary synchrotron radiation spectroscopies to study the Yb 4f electronic configuration in three representative intermediate-valence materials: YbAl3, YbInCu4, and YbCu2Si2. High-resolution x-ray absorption (PFY-XAS), resonant inelastic x-ray scattering (RIXS), and hard-x-ray photoemission (HAXPES) data all show characteristic t...

The electronic properties of Co in bulk Na0.7CoO2 and the superconducting hydrated compound Na0.35CoO2∙yH2O have been investigated by x-ray absorption spectroscopy (XAS) and resonant inelastic x-ray scattering (RIXS) using hard x rays. The XAS spectra at the Co K-edge were measured in both compounds with two different polarization directions. The c...

Changes in the electronic structure of Yb, a material whose valence is modified under pressure, are observed with remarkable detail in x-ray absorption and emission data measured between ambient conditions and 20 GPa. These changes are reproduced by a theory that essentially does not rely on experimental parameters, and includes dynamical core-hole...