Resonant Inelastic X-ray Scattering Data Research Articles

Resonant inelastic x-ray scattering data for Ruddlesden-Popper and reduced Ruddlesden-Popper nickelates

Ruddlesden-Popper and reduced Ruddlesden-Popper nickelates are intriguing candidates for mimicking the properties of high-temperature superconducting cuprates. The degree of similarity between these nickelates and cuprates has been the subject of considerable debate. Resonant inelastic x-ray scattering (RIXS) has played an important role in exploring their electronic and magnetic excitations, but these efforts have been stymied by inconsistencies between different samples and the lack of publicly available data for detailed comparison. To address this issue, we present open RIXS data on La4Ni3O10 and La4Ni3O8.

Identifying f -electron symmetries of UTe2 with O-edge resonant inelastic x-ray scattering

The recent discovery of spin-triplet superconductivity emerging from a nonmagnetic parent state in ${\mathrm{UTe}}_{2}$ has stimulated great interest in the underlying mechanism of Cooper pairing. Experimental characterization of short-range electronic and magnetic correlations is vital to understanding these phenomena. Here we use resonant inelastic x-ray scattering (RIXS), x-ray absorption spectroscopy (XAS), and atomic-multiplet-based modeling to shed light on the active debate between $5{f}^{2}6{d}^{1}$-based models with singlet crystal field states versus $5{f}^{3}$-based models that predict atomic Kramers doublets and much greater $5f$ itinerancy. The XAS and RIXS data are found to agree strongly with predictions for a $5{f}^{2}6{d}^{1}$-like valence electron configuration with weak intradimer magnetic correlations, and provide a context for interpreting recent investigations of the electronic structure and superconducting pairing mechanism.

Resonant inelastic x-ray scattering of spin-charge excitations in a Kondo system

Resonant inelastic x-ray scattering (RIXS) studies across the Ce ${M}_{5}$ edge have been carried out to investigate the electronic structure of the ferromagnetic ${\mathrm{CeAgSb}}_{2}$ Kondo system. The RIXS spectra exhibit energy loss features corresponding to final states usually observed by combining photoemission and inverse photoemission spectroscopy. At low energy loss, a clear signature of the spectral features corresponding to the spin-orbit interaction is also observed. Polarization dependence provides evidence for the ${}^{1}{S}_{0}$ symmetry singlet ground state by a total suppression of the ${f}^{0}$ final state. A simplified single-impurity Anderson model combined with full multiplet theory allows an accurate description of the spin-charge excitations. The RIXS data also reveal a strong temperature $T$ dependence of the fluorescencelike structure. We conjecture that this behavior reflects the $T$ dependence of the Kondo resonance.

Electronic structure of the frustrated diamond lattice magnet NiRh2O4

The $A$-site spinel ${\mathrm{NiRh}}_{2}{\mathrm{O}}_{4}$ is the only known realization of a spin-1 diamond lattice magnet and is predicted to host unconventional magnetic phenomena driven by frustrated nearest and next-nearest neighbor exchange as well as orbital degeneracy. Previous works found no sign of magnetic order but found a gapped dispersive magnetic excitation indicating a possible valence bond magnetic ground state. However, the presence of many competing low energy degrees of freedom and limited empirical microscopic constraints complicates further analysis. Here we carry out resonant inelastic x-ray scattering (RIXS), x-ray absorption spectroscopy (XAS), and inelastic neutron scattering (INS) to characterize the local electronic structure and lattice dynamics of ${\mathrm{NiRh}}_{2}{\mathrm{O}}_{4}$. The RIXS data can be partly described by a single-ion model for tetrahedrally coordinated ${\mathrm{Ni}}^{2+}$ and indicates a tetragonal distortion $\mathrm{\ensuremath{\Delta}}{t}_{2}=70$ meV that splits the ${t}_{2}$ orbitals into a high energy orbital singlet and lower energy orbital doublet. We identify features of the RIXS spectra that are consistent with a Rh-Ni two-site excitation indicating strong metal-metal hybridization mediated by oxygen in ${\mathrm{NiRh}}_{2}{\mathrm{O}}_{4}$. We also identify signatures of electron-phonon coupling through the appearance of phonon sidebands that dress crystal field excitations. These results establish the key energy scales relevant to the magnetism in ${\mathrm{NiRh}}_{2}{\mathrm{O}}_{4}$ and further demonstrate that covalency and lattice dynamics play essential roles in controlling the magnetic ground states of $A$-site spinels.

Resonant inelastic x-ray scattering (RIXS) spectra for ladder cuprates

The ladder compound Sr14Cu24O41 is of interest both as a quasi-one-dimensional analog of the superconducting cuprates and as a superconductor in its own right when Sr is substituted by Ca. In order to model resonant inelastic x-ray scattering (RIXS) spectra for this compound, we investigate the simpler SrCu2O3 system in which the crystal structure contains very similar ladder planes. We approximate the LDA dispersion of SrCu2O3 by a Cu only two-band tight-binding model. Strong correlation effects are incorporated by assuming an anti-ferromagnetic ground state. The available angle-resolved photoemission (ARPES) and RIXS data on the ladder compound are found to be in reasonable accord with our theoretical predictions.

Resonant inelastic x-ray scattering in metals: A diagrammatic approach

We develop a formalism to study the Resonant Inelastic X-ray Scattering (RIXS) response in metals based on the diagrammatic expansion for its cross section. The standard approach to the solution of the RIXS problem relies on two key approximations: short-range potentials and non-interacting conduction electrons. However, these approximations are inaccurate for charged particles in metals, where the long-range Coulomb interaction and dynamic screening effects are very important. In this work we study how to extract important information about collective excitations in the Coulomb plasma, plasmons and electron-hole pairs, from RIXS data. We find that single- and multi-plasmon excitations can easily be distinguished by positions of the corresponding peaks, singularities, and their intensities. We also discuss the hybrid processes, where plasmon emission is accompanied by excitation of electron-hole pairs, and study how they manifest themselves.

Crossover from Collective to Incoherent Spin Excitations in Superconducting Cuprates Probed by Detuned Resonant Inelastic X-Ray Scattering.

Spin excitations in the overdoped high temperature superconductors Tl_{2}Ba_{2}CuO_{6+δ} and (Bi,Pb)_{2}(Sr,La)_{2}CuO_{6+δ} were investigated by resonant inelastic x-ray scattering (RIXS) as functions of doping and detuning of the incoming photon energy above the Cu-L_{3} absorption peak. The RIXS spectra at optimal doping are dominated by a paramagnon feature with peak energy independent of photon energy, similar to prior results on underdoped cuprates. Beyond optimal doping, the RIXS data indicate a sharp crossover to a regime with a strong contribution from incoherent particle-hole excitations whose maximum shows a fluorescencelike shift upon detuning. The spectra of both compound families are closely similar, and their salient features are reproduced by exact-diagonalization calculations of the single-band Hubbard model on a finite cluster. The results are discussed in the light of recent transport experiments indicating a quantum phase transition near optimal doping.

Single-band model of resonant inelastic x-ray scattering by quasiparticles in high-T(c) cuprate superconductors.

We show that a simple model of noninteracting quasiparticles accurately describes resonant inelastic x-ray scattering (RIXS) experiments in the hole-doped cuprate superconductors. Band structure alone yields signatures previously attributed to collective magnetic modes, such as the dispersing peaks and nontrivial polarization dependence found in several experiments. We conclude that RIXS data can be explained without positing the existence of magnetic excitations that persist with increasing doping. In so doing we develop a formalism for RIXS in itinerant electron systems that accounts for the positively charged core hole exactly and discover a mechanism by which the core hole produces polarization dependence mimicking that of a magnetic system.

Spin-split conduction band in EuB6and tuning of half-metallicity with external stimuli

We report an Eu ${L}_{3}$-edge resonant inelastic x-ray scattering (RIXS) investigation of the electronic structure of EuB${}_{6}$. We observe that the RIXS spectral weight around 1.1 eV increases dramatically when the system is cooled below the ferromagnetic ordering temperature and follows the magnetic order parameter. This spectral feature is attributed to the intersite excitation from the local 4$f$ orbital to the spin-split 5$d$ orbital on the neighboring site, illustrating the essential role of exchange splitting of the conducting electrons. Based on our density functional theory calculations and the RIXS data, EuB${}_{6}$ at low temperature can be consistently described with a semimetallic electronic structure with incomplete spin polarization. We propose that half-metallicity in EuB${}_{6}$ can be achieved utilizing the strong tunability of the electronic structure against gate voltage, strain, and magnetic field.

Multiplet resonance lifetimes in resonant inelastic x-ray scattering involving shallow core levels

Resonant inelastic x-ray scattering (RIXS) spectra of model copper- and nickel-based transition metal oxides are measured over a wide range of energies near the M edge ($h\ensuremath{\nu}=60$--80 eV) to better understand the properties of resonant scattering involving shallow core levels. Standard multiplet RIXS calculations are found to deviate significantly from the observed spectra. However, by incorporating the self-consistently calculated decay lifetime for each intermediate resonance state within a given resonance edge, we obtain dramatically improved agreement between data and theory. Our results suggest that these textured lifetime corrections can enable a quantitative correspondence between first-principles predictions and RIXS data on model multiplet systems. This accurate model is also used to analyze resonant elastic scattering, which displays the elastic Fano effect and provides a rough upper bound for the core hole shakeup response time.

Significance of the inter-site Coulomb interaction between the O 2p and Cu 3d holes revealed by resonant inelastic x-ray scattering of Sr14Cu24O41

We have carried out resonant inelastic x-ray scattering (RIXS) measurements at the Cu K-edge on Sr14Cu24O41, which has two kinds of layers, namely, the ladder layer and the chain layer. The excitation from the Zhang–Rice singlet band to the upper Hubbard band (UHB) shows a large dispersion with a periodicity of the ladder layer. The excitation corresponding to the ligand-to-metal charge transfer is nearly dispersionless. Comparison between the RIXS data and theoretical calculations shows that the inter-site Coulomb interaction between the Cu 3d and O 2p holes plays a prominent role in the RIXS process. This interaction is expected to be important in the hole state in the ladder layer of this compound.

Resonant inelastic x-ray scattering of curium oxide

The measurements on radioactive actinide isotopes (curium-248) were performed using very small sample quantities (micrograms) to minimize the sample activity. Resonant inelastic x-ray scattering (RIXS) spectra of curium oxide at the Cm $5d$ edge were measured for the first time. RIXS data are compared with theoretical calculations using atomic multiplet theory. The results indicate that isotope curium $\ensuremath{-}248$ in the curium oxide sample has oxidation state III due to the best agreement with RIXS calculations for Cm (III) instead of those for Cm (IV).

Collapse of the Magnetic Gap of Cuprate Superconductors within a Three-Band Model of Resonant Inelastic X-Ray Scattering

We present a three-band Hubbard Hamiltonian and the associated Cu Kappa-edge resonant inelastic x-ray scattering (RIXS) spectra for electron- and hole-doped cuprates over a wide range of energy and momentum transfers. By comparing computed spectra for the unfilled case with the corresponding results for 15% electron or hole doping at two different values of the effective Hubbard parameter , generic signatures of the collapse of the magnetic gap and the characteristic momentum dependencies and evolution of the spectra with doping are identified. Available RIXS data support the gap collapse scenario for electron-doped cuprates, but the situation in hole-doped systems is found to be less clear.