J.-P. Rueff

Dynamical reconstruction of the exciton in LiF with inelastic x-ray scattering

The absorption of light by materials proceeds through the formation of excitons, which are states in which an excited electron is bound to the valence hole it vacated. Understanding the structure and dynamics of excitons is important, for example, for developing technologies for light-emitting diodes or solar energy conversion. However, there has never been an experimental means to study the time-dependent structure of excitons directly. Here, we use causality-inverted inelastic x-ray scattering (IXS) to image the charge-transfer exciton in the prototype insulator LiF, with resolutions Δt = 20.67 as (2.067 × 10−17 s) in time and Δx = 0.533 Å (5.33 × 10−11 m) in space. Our results show that the exciton has a modulated internal structure and is coherently delocalized over two unit cells of the LiF crystal (≈8 Å). This structure changes only modestly during the course of its life, which establishes it unambiguously as a Frenkel exciton and thus amenable to a simplified theoretical description. Our results resolve an old controversy about excitons in the alkali halides and demonstrate the utility of IXS for imaging attosecond electron dynamics in condensed matter.

Metal-ligand interplay in strongly correlated oxides: a parametrized phase diagram for pressure-induced spin transitions.

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-transfer effects. The spectral changes are well accounted for by changes of the ligand field acting on the d electrons and allows us to extract the d-hybridization strength, O-2p bandwidth and ionic crystal field across the magnetic transition. This approach allows first-hand insight into the mechanism of the pressure-induced spin transition.

Phonon anomalies at the valence transition of SmS: An inelastic x-ray-scattering study under pressure

The phonon dispersion curve of SmS under pressure was studied by inelastic x-ray scattering around the pressure-induced valence transition. A significant softening of the longitudinal acoustic modes propagating along the [111] direction was observed spanning a wide

Composition dependence of spin transition in (Mg,Fe)SiO3 bridgmanite

q

Intermediate valence behaviour under pressure: how precisely can we probe it by means of resonant inelastic x-ray emission?

region from (

Hard x-ray spectroscopy in Na x Co O 2 and superconducting Na x Co O 2 ∙ y H 2 O : Bulk Co electronic properties

frac{2pi}{3a},frac{2pi}{3a},frac{2pi}{3a}

Ultrafast Charge Transfer Processes Accompanying KLL Auger Decay in Aqueous KCl Solution

) up to the zone boundary as SmS becomes metallic. The largest softening occurs at the zone boundary and stays stable up to the highest measured pressure of 80 kbar while a gradual hardening of the low

Hard x-ray spectroscopy inNaxCoO2and superconductingNaxCoO2∙yH2O: Bulk Co electronic properties

q

Hard X-ray photoelectron spectroscopy on the GALAXIES beamline at the SOLEIL synchrotron

modes simultaneously appears. This phonon spectrum indicates favorable conditions for the emergence of pressure-induced superconductivity in SmS.

Spin-state-driven metal-insulator transition in (La,Sr) CoO3 under high-pressure

Abstract Spin transitions in (Mg,Fe)SiO3 bridgmanite have important implications for the chemistry and dynamics of Earth’s lower mantle, but have been complex to characterize in experiments. We examine the spin state of Fe in highly Fe-enriched bridgmanite synthesized from enstatites with measured compositions (Mg0.61Fe0.38Ca0.01)SiO3 and (Mg0.25Fe0.74Ca0.01)SiO3. Bridgmanite was synthesized at 78-88 GPa and 1800-2400 K and X‑ray emission spectra were measured on decompression to 1 bar (both compositions) and compression to 126 GPa [(Mg0.61Fe0.38Ca0.01)SiO3 only] without additional laser heating. Observed spectra confirm that Fe in these bridgmanites is dominantly high spin in the lower mantle. However, the total spin moment begins to decrease at ~50 GPa in the 74% FeSiO3 composition. These results support density functional theory predictions of a lower spin transition pressure in highly Fe-enriched bridgmanite and potentially explain the high solubility of FeSiO3 in bridgmanite at pressures corresponding to Earth’s deep lower mantle.