We investigate electronic excitations in La2−x(Br,Sr)xCuO4 using resonant inelastic x-ray scattering (RIXS) at the oxygen K edge. RIXS spectra of the hole-doped cuprates show clear momentum dependence below 1 eV. The spectral weight exhibits positive dispersion and shifts to higher energy with increasing hole concentration. Theoretical calculation of the dynamical charge structure factor on oxygen orbitals in a three-band Hubbard model is consistent with the experimental observation of the momentum and doping dependence, and therefore the dispersive mode is ascribed to intraband charge excitations which have been observed in electron-doped cuprates.PACS numbers: 71.27.+a,74.25.Jb,74.72.Gh,78.70.Ck Strongly correlated transition-metal oxides display various interesting physical properties including metalinsulator transition, high-temperature superconductivity and colossal magnetoresistance, and some of the oxides are classified into doped Mott insulators where electron correlation significantly modifies their band structure which diverges from that of the noninteracting simple metal [1]. Among the doped Mott insulators, superconducting cuprates are most intensively studied [2]. This is mainly due to the superconductivity at high transition temperature and related phenomena such as pseudogap and a competing phase with charge order [3]. In addition to the interest of superconductivity, doped cuprates are important and suitable for the study of electronic structure of the doped Mott insulator because relatively simple theoretical models with a few orbitals are applicable to describe the electronic structure near the Fermi energy. They represent the benchmark of the doped Mott insulators and the clarification of the fundamental electronic structure is essential for understanding the mechanism of the physical phenomena in the doped cuprates.In the undoped cuprates, only the spin degree of freedom contributes to the low-energy electron dynamics. When carriers are doped, the charge degree of freedom becomes active and the electron dynamics is characterized by the motion of spin and charge. Therefore, we consider that both spin and charge excitations must be investigated on equal footing in order to understand the electron dynamics characterizing the physics of the cuprates. Inelastic neutron scattering (INS) has been widely used for studying the spin dynamics in the reciprocal lattice space, and high-resolution resonant inelastic x-ray scattering (RIXS) at the Cu L 3 -edge has recently become an alternative to measure momentum-resolved spin excitations up to several hundreds meV [4,5]. Charge excitations in the doped cuprates extend to higher energy than the spin excitations and the electron correlation affects the charge excitations of the order of a few eV. Optical studies [6,7] demonstrated that spectral weight of the intraband charge excitations emerges below the charge-transfer gap in the doped cuprates and the weight characterizes the charge excitations in the doped Mott insulators. The high-energy part of mome...

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Electronic structures of electron-and hole-doped BaFe2As2 and non-doped SrFe2As2 have been studied systematically by x-ray emission spectroscopy at Fe and As K-absorption edges. The electron-and hole-doping causes slight increase of the integrated absolute difference (IAD) values of the Fe Kβ x-ray emission spectra which correlate to the local magnetic moment. Pressure decreases the IAD values and local magnetic moment, and induces the lower-spin states in these compounds. The pre-edge peak intensity of the XAS spectra at the Fe K-absorption edge increases with pressure in both compounds. This indicates an increase of the Fe 3d-As 4p hybridization. It was found that pressure induced a discontinuous increase of the pre-peak intensity of the PFY-XAS spectra at the As K-absorption edge at low pressures in the BaFe2As2 systems. Our results may suggest that the Fe 3d-As 4p hybridization plays a key role in suppressing the AFM order by the doping or pressure and fluctuation of the local magnetic moment and the electron-electron correlation may also play a role on the physical properties of the iron superconductors.

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Pressure dependence of the Ce valence in CeCu(2)Ge(2) has been measured up to 24 GPa at 300 K and to 17 GPa at 18-20 K using x-ray absorption spectroscopy in the partial fluorescence yield. A smooth increase of the Ce valence with pressure is observed across the two superconducting (SC) regions without any noticeable irregularity. The chemical pressure dependence of the Ce valence was also measured in Ce(Cu(1-x)Ni(x))(2)Si(2) at 20 K. A very weak, monotonic increase of the valence with x was observed, without any significant change in the two SC regions. Within experimental uncertainties, our results show no evidence for the valence transition with an abrupt change in the valence state near the SC II region, challenging the valence-fluctuation mediated superconductivity model in these compounds at high pressure and low temperature.