Electronic structure and resonant inelastic x-ray scattering in Ca3Ru2O7

Resonant Inelastic X-Ray Scattering (RIXS) spectra of hematite were measured at the Fe L3-edge for heteroepitaxial thin films which were undoped and doped with 1% Ti, Sn or Zn, in the energy loss range in excess of 1 eV to study electronic transitions. The spectra were measured for several momentum transfers (q), conducted at both low temperature (T=14K) and room temperature. While we can not rule out dispersive features possibly owing to propagating excitations, the coarse envelopes of the general spectra did not appreciably change shape with q, implying that the bulk of the observed L-edge RIXS intensity originates from (mostly) non-dispersive ligand field (LF) excitations. Summing the RIXS spectra over q and comparing the results at T=14 K to those at T=300 K, revealed pronounced temperature effects, including an intensity change and energy shift of the 1.4 eV peak, a broadband intensity increase of the 3-4 eV range, and higher energy features. The q-summed spectra and their temperature dependences are virtually identical for nearly all of the samples with different dopants, save for the temperature dependence of the Ti-doped sample's spectrum, which we attribute to being affected by a large number of free charge carriers. Comparing with magnetization measurements for different temperatures and dopings likewise did not show a clear correlation between the RIXS spectra and the magnetic ordering states. To clarify the excited states, we performed spin multiplet calculations which were in excellent agreement with the RIXS spectra over a wide energy range and provide detailed electronic descriptions of the excited states. The implications of these findings to the photoconversion efficiency of hematite photoanodes is discussed.

We examine theoretically the Resonant Inelastic X-ray Scattering (RIXS) spectra on nickelates by using numerically exact diagonalization techniques on the two-band Hubbard model. Other spectra such as the dynamical charge correlation function are examined to discuss what excitations appear in the RIXS. We demonstrate that the spectra which appear upon doping in the dynamical charge correlation function and the RIXS are originated from only high spin states, in contrast to the optical conductivity where the spectrum comes from both high and low spin states.

It is undeniable that novel 2D devices and heterostructures will have a lasting impact on the advancement of future technologies. However, the inherent instability of many exfoliated van der Waals (vdW) materials is a well-known hurdle yet to be overcome. Thus, the sustained interest in exfoliated vdW materials underscores the importance of understanding the mechanisms of sample degradation to establish proactive protective measures. Here, the impact of prolonged synchrotron-based X-ray beam exposure on exfoliated flakes of two contemporary vdW materials, NiPS3 and α-RuCl3, is explored using resonant inelastic X-ray scattering (RIXS) and total fluorescence yield X-ray absorption spectroscopy (XAS). In NiPS3, the resulting RIXS and XAS spectra show a suppression, then vanishing, of NiS6 multiplet excitations coupled with an upward shift of the peak energy of the XAS as a function of X-ray dose. In α-RuCl3, the signs of beam damage from the RIXS spectra are less evident. However, the post-experiment characterization of both materials using Raman spectroscopy exhibits signals of an amorphous and disordered system compared to pristine flakes; in addition, energy-dispersive X-ray spectroscopy of NiPS3 shows evidence of ligand vacancies. As synchrotron radiation is fast becoming a required probe to study 2D vdW materials, these findings lay the groundwork for the development of future protective measures for synchrotron-based prolonged X-ray beam exposure, as well as for X-ray free electron laser.

Magnetic excitations of layered cuprates studied by RIXS at Cu L3 edge

Resonant inelastic x-ray scattering in Ca3LiOsO6 from first-principles

Resonant inelastic X-ray scattering (RIXS) was used to collect Mn K pre-edge spectra and to study the electronic structure in oxides, molecular coordination complexes, as well as the S1 and S2 states of the oxygen-evolving complex (OEC) of photosystem II (PS II). The RIXS data yield two-dimensional plots that can be interpreted along the incident (absorption) energy or the energy transfer axis. The second energy dimension separates the pre-edge (predominantly 1s to 3d transitions) from the main K-edge, and a detailed analysis is thus possible. The 1s2p RIXS final-state electron configuration along the energy transfer axis is identical to conventional L-edge absorption spectroscopy, and the RIXS spectra are therefore sensitive to the Mn spin state. This new technique thus yields information on the electronic structure that is not accessible in conventional K-edge absorption spectroscopy. The line splittings can be understood within a ligand field multiplet model, i.e., (3d,3d) and (2p,3d) two-electron interactions are crucial to describe the spectral shapes in all systems. We propose to explain the shift of the K pre-edge absorption energy upon Mn oxidation in terms of the effective number of 3d electrons (fractional 3d orbital population). The spectral changes in the Mn 1s2p(3/2) RIXS spectra between the PS II S1 and S2 states are small compared to that of the oxides and two of the coordination complexes (Mn(III)(acac)3 and Mn(IV)(sal)2(bipy)). We conclude that the electron in the step from S1 to S2 is transferred from a strongly delocalized orbital.

Valence-to-core resonant inelastic X-ray scattering (RIXS) and high energy resolution fluorescence detection (HERFD) X-ray absorption measurements were performed at the U L3 edges of UO2 and UO2(NO3)2(H2O)6. The results are compared with model calculations based on the local-density-approximation formalism, taking into account Coulomb interaction U (LDA + U). We show that despite strong 5f-5f electronic correlations in the studied systems and the use of core-level excitations in the intermediate stage of the spectroscopic process, the RIXS technique probes a convolution of the single-particle densities of states in the valence and conduction bands. For UO2, the detected crystal-field splitting between the U 6d eg and t2g orbitals from the RIXS spectra (∼3.5 eV) is larger than that previously derived from optical spectroscopy. Furthermore, by using an example of the U0.75Pu0.25O2 mixed oxide, we show that the RIXS technique at the U L3 edges is sensitive to the substitution of U with other actinide, in contrast to conventional X-ray absorption methods. That is, due to changes in the occupied part rather than in the unoccupied part of the U 6d states caused by the substitution.

We report on a combined theoretical and experimental study of core-excitation spectra of gas and liquid phase methanol as obtained with the use of X-ray absorption spectroscopy (XAS) and resonant inelastic X-ray scattering (RIXS). The electronic transitions are studied with computational methods that include strict and extended second-order algebraic diagrammatic construction [ADC(2) and ADC(2)-x], restricted active space second-order perturbation theory, and time-dependent density functional theory-providing a complete assignment of the near oxygen K-edge XAS. We show that multimode nuclear dynamics is of crucial importance for explaining the available experimental XAS and RIXS spectra. The multimode nuclear motion was considered in a recently developed "mixed representation" where dissociative states and highly excited vibrational modes are accurately treated with a time-dependent wave packet technique, while the remaining active vibrational modes are described using Franck-Condon amplitudes. Particular attention is paid to the polarization dependence of RIXS and the effects of the isotopic substitution on the RIXS profile in the case of dissociative core-excited states. Our approach predicts the splitting of the 2a″ RIXS peak to be due to an interplay between molecular and pseudo-atomic features arising in the course of transitions between dissociative core- and valence-excited states. The dynamical nature of the splitting of the 2a″ peak in RIXS of liquid methanol near pre-edge core excitation is shown. The theoretical results are in good agreement with our liquid phase measurements and gas phase experimental data available from the literature.

Proton transfer processes form the foundation of many chemical processes. In excited-state intramolecular proton transfer (ESIPT) processes, ultrafast proton transfer is impulsively initiated through light. Here, we explore time-dependent coupled atomic and electronic motions during and following ESIPT through computational time-resolved resonant inelastic X-ray scattering (RIXS). Excited-state ab initio molecular dynamics simulations combined with time-dependent density functional theory calculations were performed for a model ESIPT system, 10-hydroxybenzo[h]quinoline, to obtain transient RIXS signatures. The RIXS spectra at both the nitrogen and oxygen K-edges were computed to resolve the electronic and atomic structural dynamics from both the proton donor and acceptor perspective. The results demonstrate that RIXS provides unprecedented details of the local electronic structure, the coupling between different core and valence excited electronic states, and the reorganization of the electronic structure coupled to the proton transfer process. We also develop a spectroscopic ruler correlating spectral shifts of a RIXS peak to the proton transfer distance during ESIPT. This work highlights the exciting potential of time-resolved RIXS experiments at newly commissioned soft X-ray free electron laser facilities for measuring coupled electronic and structural changes during ultrafast chemical processes.

Electronic structure and resonant inelastic x-ray scattering in the mixed [formula omitted]-[formula omitted] transition-metal oxides Sr[formula omitted]CuIrO[formula omitted], Sr[formula omitted]CuPtO[formula omitted], and Sr[formula omitted]ZnIrO[formula omitted

Electronic structure and resonant inelastic x-ray scattering in GaTa4Se8

We analyze the resonant inelastic x-ray scattering (RIXS) spectra at the $K$ edge of Mn in the antiferromagnetic insulating manganite ${\text{LaMnO}}_{3}$. We make use of the Keldysh-type Green's function formalism, in which the RIXS intensity is described by a product of an incident-photon-dependent factor and a density-density correlation function in the $3d$ states. We calculate the former factor using the $4p$ density of states given by an ab initio band-structure calculation and the latter using a multiorbital tight-binding model. The ground state of the model Hamiltonian is evaluated within the Hartree-Fock approximation. Correlation effects are treated within the random-phase approximation (RPA). We obtain the RIXS intensity in a wide range of energy loss (2--15 eV). The spectral shape is strongly modified by the RPA correlation, showing good agreement with the experiments. The incident-photon-energy dependence also agrees well with the experiments. The present mechanism that the RIXS spectra arise from band-to-band transitions to screen the core-hole potential is quite different from the orbiton picture previously proposed, enabling a comprehensive understanding of the RIXS spectra.

Dy 2 O 3 and Dy metal's resonant inelastic x‐ray scattering (RIXS) spectra were measured in the Beijing Synchrotron Radiation Facility. As a bulk sensitive probe and two‐photon process, RIXS provides more information on the electronic structure of matter. In this full RIXS experiment, the 2p 6 4f n → 2p 5 4f n 5d 1 (2p 5 4f n + 1 5d 0 ) → 2p 6 3d 9 4f n 5d 1 (2p 6 3d 9 4f n + 1 5d 0 ) channel of two samples (Dy 2 O 3 and Dy metal) was studied. Further comparison shows that there are many differences in the RIXS spectra. Dy metal has only a single resonance and its 5d band is broader than that of Dy 2 O 3 . In the resonant regime, it has a lower final state energy, whereas in the non‐resonant regime it exceeds Dy 2 O 3 . This causes a broader bandwidth of the main final state B and a narrower bandwidth in the resonant and non‐resonant regime. The pre‐edge structure in Dy L 3 absorption spectra was also resolved using RIXS, which cannot be seen in conventional XAS owing to 2p core hole lifetime broadening. Copyright © 2005 John Wiley & Sons, Ltd.

Resonant inelastic x-ray scattering (RIXS) is used to study the electronic structure of NiF2, which is the most ionic of the nickel compounds. RIXS can be viewed as a coherent two-steps process involving the absorption and the emission of x-rays. The soft x-ray absorption spectrum (XAS) at the metal L2,3 edge indicate the importance of atomic multiplet effects. RIXS spectra at L2,3 contain clearly defined emission peaks corresponding to d-excited states of Ni2+ at energies few eV below the elastic emission, which is strongly suppressed. These results are confirmed by atomic multiplet calculations using the Kramers-Heisenberg formula for RIXS processes. For larger energy losses, the emission spectra have a broad charge-transfer peak that results from the decay of hybridized Ni(3d)-F(2p) valence states. This is confirmed by comparison of the absorption and emission spectra recorded at the nickel L and fluorine K edges with F p and Ni d partial density of states using LDA + U calculations.

We report a resonant inelastic x-ray scattering (RIXS) study of crystalline CeB6. Ce Lα1,2 RIXS was measured with excitation energies resonant with the Ce L3-edge. A lifetime-broadening suppressed x-ray absorption near-edge structure (LBS-XANES), which successfully reproduced the Lα1,2 RIXS spectra over wide ranges of excitation and emission energies, was simulated using the SIM-RIXS program. A pre-edge structure in the LBS-XANES can be resolved, and many-body effects were suggested in the Lα1,2 RIXS around the Ce L3-edge energy. No convincing signs of Ce (II) or Ce (IV) states were observed in the LBS-XANES. Ce Lγ4 RIXS was measured at 302 K and 28 K with excitation energies across the Ce L1-edge. The interactions of p-valence electrons between Ce and B6 were found to be considerably small, regardless of temperature. Thus, the electronic state of CeB6 was concluded to be suitably described as a nominally Ce(4f 1)3+(e−)(B6)2− system with some hybridization among all valence orbitals of Ce and B.