Biomedical subjects

A Chainani

Publications and source records attributed to A Chainani.

At least 19 recordsLinked to original sources

PubMed2006

Bulk- and surface-sensitive high-resolution photoemission study of two mott-hubbard systems: SrVO3 and CaVO3.

We study the electronic structure of Mott-Hubbard systems SrVO3 and CaVO3 with bulk and surface-sensitive high-resolution photoemission spectroscopy, using a vacuum ultraviolet laser, synchrotron radiation, and a discharge lamp (hv = 7-21 eV). A systematic suppression of the density of states (DOS) within approximately 0.2 eV of the Fermi level (EF) is found on decreasing photon energy, i.e., on increasing bulk sensitivity. The coherent band in SrVO3 and CaVO3 is shown to consist of surface and bulk-derived features, separated in energy. The stronger distortion on surface of CaVO3 compared to SrVO3 leads to a higher surface metallicity in the coherent DOS at EF, consistent with recent theory.

Journal Article↗

PubMed2005

Temperature-dependent Luttinger surfaces.

The Luttinger surface of an organic metal (TTF-TCNQ), possessing charge order and spin-charge separated band dispersions, is investigated using temperature-dependent angle-resolved photoemission spectroscopy. The Luttinger surface topology, obtained from momentum distribution curves, changes from quasi-2D (dimensional) to quasi-1D with temperature. The high temperature quasi-2D surface exhibits 4kF charge-density-wave (CDW) superstructure in the TCNQ derived holon band, in the absence of 2kF order. Decreasing temperature results in quasi-1D nested 2kF CDW order in the TCNQ spinon band and in the TTF surface. The results establish the link in momentum space between charge order and spin-charge separation in a Luttinger liquid.

Journal Article↗

PubMed2005

Evidence for suppressed screening on the surface of high temperature La(2-x)SrxCuO4 and Nd2(2-x)CexCuO4 superconductors.

Hard x-ray photoemission spectroscopy (PES) of Cu core electronic states, with a probing depth of approximately 60 A, is used to show that the Zhang-Rice singlet feature is present in La2CuO4 but is absent in Nd2CuO4. Hole and electron doping in La(2-x)SrxCuO4 (LSCO) and Nd(2-x)CexCuO4 (NCCO) result in new well-screened features which are missing in soft x-ray PES. Impurity Anderson model calculations establish screening from doped states as its origin, which is strongly suppressed within 15 A of the surface. Complemented with x-ray absorption spectroscopy, the small chemical-potential shift in core levels (approximately 0.2 eV) are shown to be consistent with modifications of valence and conduction band states spanning the band gap (approximately 1 eV) upon hole and electron doping in LSCO and NCCO.

Journal Article↗

PubMed2004

Nature of the well screened state in hard X-ray Mn 2p core-level photoemission measurements of La1-xSrxMnO3 films.

Using hard x-ray (HX; hnu=5.95 keV) synchrotron photoemission spectroscopy (PES), we study the intrinsic electronic structure of La(1-x)Sr(x)MnO(3) (LSMO) thin films. Comparison of Mn 2p core-levels with soft x-ray (SX; hnu approximately 1000 eV) PES shows a clear additional well-screened feature only in HX PES. Takeoff-angle dependent data indicate its bulk (> or =20 A) character. The doping and temperature dependence track the ferromagnetism and metallicity of the LSMO series. Cluster model calculations including charge transfer from doping-induced states show good agreement, confirming this picture of bulk properties reflected in Mn 2p core-levels using HX PES.

Journal Article↗

PubMed2001

Fermi surface sheet-dependent superconductivity in 2H-NbSe2.

High-resolution angle-resolved photoemission spectroscopy was used to study the superconducting energy gap and changes in the spectral function across the superconducting transition in the quasi-two-dimensional superconductor 2H-NbSe2. The momentum dependence of the superconducting gap was determined on different Fermi surface sheets. The results indicate Fermi surface sheet-dependent superconductivity in this low-transition temperature multiband system and provide a description consistent with thermodynamic measurements and the anomalous de Haas-van Alphen oscillations observed in the superconducting phase. The present data suggest the importance of Fermi surface sheet-dependent superconductivity in explaining exotic superconductivity in other multiband systems with complex Fermi surface topology, such as the borides and f-electron superconductors.

Journal Article↗

PubMed2000

Photoemission spectroscopy of the strong-coupling superconducting transitions in lead and niobium

We study the changes in the electronic structure associated with low- T(c) strong-coupling superconducting transitions in Pb and Nb using ultrahigh-resolution (2.3 meV) temperature-dependent (5.3-12.0 K) photoemission spectroscopy. We observe peaks in the density of states on entering the superconducting-phase accompanying gap formation and spectacular redistribution of spectral weight at low energy scales as a function of temperature. The well-known peak-dip feature of the high- T(c) cuprates is seen in Pb, making it a characteristic of strong-coupling superconductivity.

Journal Article↗

PubMed1996