Hirofumi Namatame

Doping dependence of the electronic structure of superconducting and non-superconducting oxides: High-energy spectroscopic studies

Abstract The electronic structure of electron- and hole-doped of Cu, Bl, and related 3d-transition-metal oxides has been studied by photoemission spectroscopy. In every system, carrier doping induces new states within the band gap of the parent compound. These “mid-gap states” are distributed mainly below and above the Fermi level for electron and hole doping, respectively. At low doping levels, doped carriers are localized around the impurities or defects, whereas they become itinerant at high doping levels reflecting the first affinity level or ionization state of the parent compound. The electronic structure of superconducting oxides is characterized by the high mobility of itinerant carriers.

Photoemission Study of the Electronic Structure of the Ferromagnetic Cr1-δTe System

The electronic structure of Cr1-δTe (δ=0.05, 0.25, 0.375) has been studied by photoemission spectroscopy. Structures near the Fermi level are qualitatively explained by the density of states (DOS) given by band-structure calculations, but significant discrepancies exist in the higher binding energy region. Configuration-interaction cluster-model calculations have been performed and the overall experimental features have been explained, indicating significant electron correlation effects in these compounds.

Photoemission spectroscopic study of copper-oxide superconductors and related materials

The electronic structure of high-Tc superconductors and related materials is studied by photoemission spectroscopy and Bremsstrahlung Isochromat spectroscopy. In the solid solution (La,Sr)2CuO4, (Nd,Ce)2CuO4, and (La,Sr)2NiO4 systems, the valence band spectra do not shift as a function of the doping concentration, which suggests that EF is pinned by the states within the charge-transfer gap and that the rigid band description is not appropriate in considering the metal-insulator transition in these systems.

X-Ray Absorption Study of the Metal-Nonmetal Transition in NiS and Ni1-xMxS (M=Fe and Co)

We have studied the electronic structure of NiS using Ni 2p X-ray absorption spectroscopy and subsequent clustermodel analysis. The results indicate that with Fe substitution or with decreasing temperature, the S 3p-to-Ni 3d chargetransfer energy increases and the Ni 3d-S 3p transfer integral decreases leading to the increase in the band gap and with Co substitution the band widths increase through the Ni 3d-to-Co 3d hybridization leading to the collapse of the band gap.

Photoemission and X-ray absorption study of la1-xsrxmno3

The electronic structure of La1-xSrxMnO3 has been investigated by photoemission and X-ray absorption spectroscopy. The spectra have been analyzed using a configuration interaction cluster model. Deduced parameters show that the band gap of LaMnO3 is of the p-d gap type while that of SrMnO3 has also considerable p-p character. The shift of the Fermi level with doping does not follow the simple rigid band picture. The photoemission spectra of SrMnO3 doped with electrons show the appearance of in-gap states in the band gap of SrMnO3.