Occupied and unoccupied electronic states in a layered perovskite superconductor without copper: band dispersions van Hove singularity and hole states in Sr2RuO4

摘要

Abstract: The occupied and unoccupied electronic structure ofhigh quality single crystals of the copper- freelayered perovskite superconductor Sr$-2$/RuO$-4$/ hasbeen measured for the first time. Angle-resolvedphotoemission spectroscopy with high energy and angleresolution determined band dispersions along theprinciple directions of the projected Brillouin zone ofthe (001) surface. The highlight of these spectra isthe observation and characterization of an extended vanHove singularity. The singularity is located 17 meVbelow the Fermi level and extends around the $OBAR@Mpoint for around 0.2 angstrom$+$MIN@1$/ along both$OBAR$Gamma@-$OBAR@M-$OBAR@Gamma and$OBAR@X-$OBAR@M-$OBAR@X. Dispersions of the near-Fermilevel states in Sr$-2$/RuO$-4$/ reveal 3 bands whichcross the Fermi level giving rise to 3 Fermi surfaces;1 electron-like Fermi surface around the $OBAR$Gammapoint and 2 hole-like surfaces encircling the $OBAR@Xpoint. The topology of the empirically determined Fermisurfaces is found to be in qualitative agreement withlocal density approximation band structurecalculations. Photoemission of the full valence band ofSr$-2$/RuO$-4$/ are also presented. The total valenceband width is approximately 9 eV, the density of statesat the Fermi level derived from photoemission is 1.3states/(eV cell) and has an 80%/20% mix of metal toligand character. Polarization-dependent O1s NEXAFSperformed on Sr$-2$/RuO$-4$/ demonstrate mainly holestates at the Fermi level in orbitals in the RuO$-2$/planes. Electron correlations among Ru 4d levels inSr$-2$/RuO$-4$/ are argued to have a lesser impact thanthat of 3d levels in the cuprates. !24