We report a resonant inelastic x-ray scattering (RIXS) study of charge excitations in the electron-doped high-T(c) superconductor Nd1.85 Ce0.15 CuO4. The intraband and interband excitations across the Fermi energy are separated for the first time by tuning the experimental conditions properly to measure charge excitations at low energy. A dispersion relation with q-dependent width emerges clearly in the intraband excitation, while the intensity of the interband excitation is concentrated around 2 eV near the zone center. The experimental results are consistent with theoretical calculation of the RIXS spectra based on the Hubbard model.

The charge disproportionation and the magnetic properties of Sr 3 Fe 2 O 7 , which has a doublelayered perovskite structure, have been investigated. From 57 Fe Mössbauer measurements, the Néel temperature T N and the critical temperature for the charge disproportionation reaction (2Fe 4+ → Fe 3+ + Fe 5+ ) are determined to be 120 K ± 2 K and 343 K ± 10 K, respectively. Above 343 K, spectra clearly show a Fe 4+ singlet. The 57 Fe Mössbauer spectrum at 4.5 K under externally applied longitudinal magnetic field consists of four magnetically split components and is similar to the spectrum obtained from CaFeO 3 with a helical spin structure. With an increase the external magnetic field, the relative intensity of the 2nd and 5th absorption peaks increases, which implies that the magnetic moments of Fe have a tendency to form a texture perpendicular to the direction of the external magnetic field.The crystal structure, magnetic and electronic properties of the high spin d 4 (t 3 2g e 1 g ) iron perovskites have been studied extensively in recent decades. SrFeO 3 , CaFeO 3 , Sr 2 FeO 4 and Sr 3 Fe 2 O 7 are typical perovskites with the high spin d 4 which display a wide variety of magnetic and electric properties. SrFeO 3 has a cubic perovskite structure, in which the angle of Fe-O-Fe is 180 • , and does not show any lattice distortion down to 4.2 K, showing a metallic-like conductivity. 1) SrFeO 3 shows an antiferromagnetic order with a helical spin structure below 127 K. Fe spins align parallel in (111) and tilt about 40 • between neighboring (111) planes. 2) The strong covalency of σ * [e g − O(2s, 2p σ ) − e g ] interactions in SrFeO 3 leads to the formation of a band and electron delocalization. 3) CaFeO 3 , with a distorted perovskite structure in which the angle of Fe-O-Fe is about 160 • , shows a charge disproportionation (CD) reaction (2Fe 4+ → Fe 3+ + Fe 5+ ) below 290 K due to a conduction band narrower than that of SrFeO 3 . 4) The 57 Fe Mössbauer spectrum obtained from CaFeO 3 below 290 K indicates that the iron ions occupy two nonequivalent sites as Fe 3+ and Fe 5+ , which show different hyperfine interaction parameters. 5, 6) The 57 Fe Mössbauer spectrum of cubic SrFeO 3 shows only one sextet at 4.2 K. 7) Sr 2 FeO 4 has a K 2 NiF 4 -type structure consisting of isolated FeO 6 octahedra sheets, and displays no CD. 8) Sr 3 Fe 2 O 7 consists of isolated double sheets of FeO 6 octahedra, which is called a layered perovskite structure. Sr 3 Fe 2 O 7 is antiferromagnetic below T N = 120 K and shows a CD reaction, 8,9) although the critical temperature of CD has not yet been determined precisely. The 57 Fe Mössbauer spectrum of Sr 3 Fe 2 O 6.92 at 295 K is reported to be a superposition of Fe 4+ and Fe

Mott gap excitations in the optimally doped high-T(c) superconductor YBa(2)Cu(3)O(7-delta) (T(c)=93 K) have been studied by the resonant inelastic x-ray scattering method. Anisotropic spectra in the ab plane are observed in a twin-free crystal. The excitation from the one-dimensional CuO chain is enhanced at 2 eV near the zone boundary of the b* direction, while the excitation from the CuO2 plane is broad at 1.5-4 eV and almost independent of the momentum transfer. Theoretical calculations based on the one-dimensional and two-dimensional Hubbard model reproduces the observed spectra when different values of the on-site Coulomb energy are assumed. The Mott gap of the CuO chain site is found to be much smaller than that of the CuO2 plane site.

The rusts formed on mild steel (15-year exposure) and weathering steel (32-year exposure) exposed to an industrial environment have been characterized by means of X-ray diffraction technique and 57 Fe Mössbauer spectroscopy. By using an X-ray diffraction method, it is suggested that the rusts formed on both steels consist of the crystalline α-FeOOH, γ -FeOOH and an X-ray amorphous phase, which gives no peak to X-ray diffraction pattern. The amount of the X-ray amorphous phase exceeds 50% of the total amount of the rust. The 57 Fe Mössbauer spectra observed at 10 K indicate that the rust contains only α-FeOOH, γ -FeOOH and Fe 3−δ O 4 (γ -Fe 2 O 3 ) for mild steel, and only α-FeOOH and γ -FeOOH for weathering steel. The X-ray amorphous substance in the rust layer formed on mild steel possesses the structures of mainly α-FeOOH showing superparamagnetism owing to its small particle size, and Fe 3−δ O 4 (γ -Fe 2 O 3 ). They are contained both in the inner rust layer and in the outer rust layer. The X-ray amorphous phase in the rust layer formed on weathering steel is mainly α-FeOOH.

We report a Cu K-edge resonant inelastic x-ray scattering (RIXS) study of orbital excitations in KCuF3. By performing the polarization analysis of the scattered photons, we disclose that the excitation between the eg orbitals and the excitations from t2g to eg exhibit distinct polarization dependence. The polarization dependence of the respective excitations is interpreted based on a phenomenological consideration of the symmetry of the RIXS process that yields a necessary condition for observing the excitations. In addition, we show that the orbital excitations are dispersionless within our experimental resolution.