<title>Occupied and unoccupied electronic states in a layered perovskite superconductor without copper: band dispersions, van Hove singularity, and hole states in Sr<formula><inf><roman>2</roman></inf></formula>RuO<formula><inf><roman>4</roman></inf></formula></title>

Abstract

The occupied and unoccupied electronic structure of high quality single crystals of the copper- free layered perovskite superconductor Sr2RuO4 has been measured for the first time. Angle-resolved photoemission spectroscopy with high energy and angle resolution determined band dispersions along the principle directions of the projected Brillouin zone of the (001) surface. The highlight of these spectra is the observation and characterization of an extended van Hove singularity. The singularity is located 17 meV below the Fermi level and extends around the M point for around 0.2 angstrom-1 along both (Gamma) -M-Gamma and X-M-X. Dispersions of the near-Fermi level states in Sr2RuO4 reveal 3 bands which cross the Fermi level giving rise to 3 Fermi surfaces; 1 electron-like Fermi surface around the (Gamma) point and 2 hole-like surfaces encircling the X point. The topology of the empirically determined Fermi surfaces is found to be in qualitative agreement with local density approximation band structure calculations. Photoemission of the full valence band of Sr2RuO4 are also presented. The total valence band width is approximately 9 eV, the density of states at the Fermi level derived from photoemission is 1.3 states/(eV cell) and has an 80%/20% mix of metal to ligand character. Polarization-dependent O1s NEXAFS performed on Sr2RuO4 demonstrate mainly hole states at the Fermi level in orbitals in the RuO2 planes. Electron correlations among Ru 4d levels in Sr2RuO4 are argued to have a lesser impact than that of 3d levels in the cuprates.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.