Low-energy V t2g orbital excitations in NdVO3.

The electronic structure of NdVO(3) and YVO(3) has been investigated as a function of sample temperature using resonant inelastic soft x-ray scattering at the V L(3)-edge. Most of the observed spectral features are in good agreement with an atomic crystal-field multiplet model. However, a low energy feature is observed at ∼ 0.4 eV that cannot be explained by crystal-field arguments. The resonant behaviour of this feature establishes it as due to excitations of the V t(2g) states. Moreover, this feature exhibits a strong sample temperature dependence, reaching maximum intensity in the orbitally-ordered phase of NdVO(3), before becoming suppressed at low temperatures. This behaviour indicates that the origin of this feature is a collective orbital excitation, i.e. the bi-orbiton.

The band structure of WO3 and non-rigid-band behaviour in Na0.67WO3 derived from soft x-ray spectroscopy and density functional theory.

The electronic structure of single-crystal WO3 and Na0.67WO3 (a sodium-tungsten bronze) has been measured using soft x-ray absorption and resonant soft x-ray emission oxygen K-edge spectroscopies. The spectral features show clear differences in energy and intensity between WO3 and Na0.67WO3. The x-ray emission spectrum of metallic Na0.67WO3 terminates in a distinct Fermi edge. The rigid-band model fails to explain the electronic structure of Na0.67WO3 in terms of a simple addition of electrons to the conduction band of WO3. Instead, Na bonding and Na 3s-O 2p hybridization need to be considered for the sodium-tungsten bronze, along with occupation of the bottom of the conduction band. Furthermore, the anisotropy in the band structure of monoclinic γ-WO3 revealed by the experimental spectra with orbital-resolved geometry is explained via density functional theory calculations. For γ-WO3 itself, good agreement is found between the experimental O K-edge spectra and the theoretical partial density of states of O 2p orbitals. Indirect and direct bandgaps of insulating WO3 are determined from extrapolating separations between spectral leading edges and accounting for the core-hole energy shift in the absorption process. The O 2p non-bonding states show upward band dispersion as a function of incident photon energy for both compounds, which is explained using the calculated band structure and experimental geometry.

Electronic structure of N,N'-ethylene-bis(1,1,1-trifluoropentane-2,4-dioneiminato)-copper(II) (Cu-TFAC), from soft X-ray spectroscopies and density functional theory calculations.

The element and orbital-specific electronic structure of thin films of the organic material N,N'-ethylene-bis(1,1,1-trifluoropentane-2,4-dioneiminato)-copper(II) (designated as Cu-TFAC) has been studied using a combination of synchrotron radiation-excited resonant X-ray emission spectroscopy, X-ray photoelectron spectroscopy, X-ray absorption spectroscopy and density functional theory calculations. Furthermore, resonant X-ray emission at the carbon K-edge was used to measure the density of states for individual C sites in the molecule.