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Investigating LaNi 12x M x O 3 (M Mn and Fe), we identify a characteristic evolution of the spectral function with increasing disorder in the presence of strong interaction effects across the metal-insulator transition. We discuss these results vis-à-vis existing theories of electronic structure in the simultaneous presence of disorder and interaction. [S0031-9007(98)05947-X]

During the last 10 years various types of soft x-ray monochromators have been developed, which are optically based on the plane grating focusing condition introduced in 1980. These instruments as well as those using the original 1980 optical configuration are reviewed and compared to the other type of high performance soft x-ray grating monochromator, the Rowland circle based spherical grating monochromator (SGM). Performance data of a plane grating monochromator (HE-PGM3), which was recently commissioned at BESSY and which offers a broad spectral range (40-2000 eV) and very high spectral resolution (up to EIAE-10 000) are given in more detail. The performance of grating and crystal monochromators is compared in the l-2 keV photon energy range.

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We present high-energy spectroscopy results on the occupied and unoccupied electronic structures of the strongly anisotropic compounds MoO 3 and K 0.3 MoO 3 near the Fermi level. X-ray photoemission reveals a close similarity of the valence-band spectra in both materials. The metal K 0.3 MoO 3 shows an additional Mo 4d-derived conduction band whose population is achieved by electron transfer from K to Mo. This is concluded from studies on intentional surface doping of insulating MoO 3 which leads to the occurrence of Mo 4d-like defect states near the Fermi level. Information on the unoccupied states and their orbital symmetries was obtained by polarization-dependent x-ray absorption spectroscopy. These experiments confirm previous descriptions of the electronic structure in terms of a molecular-orbital picture. For K 0.3 MoO 3 , strong local Mo 4d-O 2p bonding is not only found along the chain direction but also perpendicular to it. This finding is reminiscent of earlier band calculations, which found the chains to form pairs by pronounced transverse hybridization, with the overall bandwidth remaining one dimensionally anisotropic. This adds an important aspect to the discussion on possible Luttinger-liquid physics in the low-dimensional Mo bronzes. ͓S0163-1829͑99͒02636-3͔ PRB 60 M. SING et al.