Evidence for mass renormalization in LaNiO$"" sub 3_: an in situ soft x-ray photoemission study of epitaxial films

We investigate the electronic structure of high-quality single-crystal LaNiO$_3$ (LNO) thin films using in situ photoemission spectroscopy (PES). The in situ high-resolution soft x-ray PES measurements on epitaxial thin films reveal the intrinsic electronic structure of LNO. We find a new sharp feature in the PES spectra crossing the Fermi level, which is derived from the correlated Ni 3$d$ $e_g$ electrons. This feature shows significant enhancement of spectral weight with decreasing temperature. From a detailed analysis of resistivity data, the enhancement of spectral weight is attributed to increasing electron correlations due to antiferromagnetic fluctuations.Comment: 4 pages, 4 figures. submitted to Phys. Rev.

Photoemission evidence for a Mott-Hubbard metal-insulator transition in VO2_2

The temperature ($T$) dependent metal-insulator transition (MIT) in VO$_2$ is investigated using bulk sensitive hard x-ray ($\sim$ 8 keV) valence band, core level, and V 2$p-3d$ resonant photoemission spectroscopy (PES). The valence band and core level spectra are compared with full-multiplet cluster model calculations including a coherent screening channel. Across the MIT, V 3$d$ spectral weight transfer from the coherent ($d^1\underbar{\it {C}}$ final) states at Fermi level to the incoherent ($d^{0}+d^1\underbar{\it {L}}$ final) states, corresponding to the lower Hubbard band, lead to gap-formation. The spectral shape changes in V 1$s$ and V 2$p$ core levels as well as the valence band are nicely reproduced from a cluster model calculations, providing electronic structure parameters. Resonant-PES finds that the $d^1\underbar{\it{L}}$ states resonate across the V 2$p-3d$ threshold in addition to the $d^{0}$ and $d^1\underbar{\it {C}}$ states. The results support a Mott-Hubbard transition picture for the first order MIT in VO$_2$.Comment: 6 pages, 3 figures. to be published in Phys. Rev.

Self-Energy Effects on the Low- to High-Energy Electronic Structure of SrVO3

The correlated electronic structure of SrVO3 has been investigated by angle-resolved photoemission spectroscopy using in-situ prepared thin films. Pronounced features of band renormalization have been observed: a sharp kink ~60 meV below the Fermi level (EF) and a broad so-called "high-energy kink" ~0.3 eV below EF as in the high-Tc cuprates although SrVO3 does not show magnetic fluctuations. We have deduced the self-energy in a wide energy range by applying the Kramers-Kronig relation to the observed spectra. The obtained self-energy clearly shows a large energy scale of ~0.7 eV which is attributed to electron-electron interaction and gives rise to the ~0.3 eV "kink" in the band dispersion as well as the incoherent peak ~1.5eV below EF. The present analysis enables us to obtain consistent picture both for the incoherent spectra and the band renormalization.Comment: 5 pages, 3 figure

Coexistence of Bloch electrons and glassy electrons in Ca10(Ir4As8)(Fe2_xIrxAs2)5 revealed by angle-resolved photoemission spectroscopy

Angle-resolved photoemission spectroscopy of Ca10(Ir4As8)(Fe2_xIrxAs2)5 shows that the Fe 3d electrons in the FeAs layer form the hole-like Fermi pocket at the zone center and the electron-like Fermi pockets at the zone corners as commonly seen in various Fe-based superconductors. The FeAs layer is heavily electron doped and has relatively good two dimensionality. On the other hand, the Ir 5d electrons are metallic and glassy probably due to atomic disorder related to the Ir 5d orbital instability. Ca10(Ir4As8)(Fe2_xIrxAs2)5 exhibits a unique electronic state where the Bloch electrons in the FeAs layer coexist with the glassy electrons in the Ir4As8 layer.Comment: 4 pages, 3 figure

Selective expression of RT6 superfamily in human bronchial epithelial cells.

RT6 proteins are glycosylphosphatidylinositol (GPI)-linked alloantigens that are localized to cytotoxic T lymphocytes and that have nicotinamide adenine dinucleotide glycohydrolase and adenosine diphosphate (ADP)-ribosyltransferase activities. In view of the importance of GPI-linked surface proteins in mediating interactions of cells with their milieu, and the varied functions of airway cells in inflammation, we undertook the present study to determine whether human homologues of the RT6 superfamily of ADP-ribosyltransferases (ART) are expressed in pulmonary epithelial cells. We hypothesized that these surface proteins or related family members may be present in cells that interact with inflammatory cells, and that they may thereby be involved in intercellular signaling. Using in situ analysis and Northern blot analysis, we identified ART1 messenger RNA (mRNA) in airway epithelial cells. As expected for GPI-anchored proteins, the localization of ART1 at the apical surface of ciliated epithelial cells was demonstrated by staining with polyclonal anti-ART1 antibody, and was confirmed by loss of this immunoreactivity after treatment with phosphatidylinositol-specific phospholipase C (PI-PLC), which selectively cleaves GPI anchors and releases proteins from the plasma membrane. Using in situ hybridization with specific ART3 and ART4 oligonucleotides, we also identified two additional members of the RT6 superfamily in epithelial cells. In accord with these findings, we identified ART3 and ART4 mRNAs through reverse transcription- polymerase chain reaction of polyadenine-positive RNA from human trachea. Interestingly, these proteins appeared to be preferentially localized to the airway epithelium. The localized expression of these members of the RT6 superfamily in human pulmonary epithelial cells may reflect a role for them in cell-cell signaling during immune responses within the airwa