Investigation of the Electronic Structure of High-Temperature Superconductors by Polarized X-Ray Absorption Spectroscopy

Abstract

The electronic structure of high-temperature superconductors near the Fermi level which is of primary interest for the understanding of the mechanism of superconductivity, is not yet well understood. Most theoretical investigations deal with Cu3dx−y and O2px,y orbitals at EF, but whether or not O2pz and Cu3d3z−r orbitals contribute to states at EF, is still under discussion. The contribution of states with out-of-plane orbital character has been investigated by polarized x-ray absorption spectroscopy (XAS) on HTSC single crystals. For La2−xSrxCuO4 a small contribution from O2pz orbitals (8% of holes in O2p valence band states) was observed which increased to about 13% on 30% Sr doping. In n-type doped HTSC there is no clear evidence for O2pz orbitals at EF, but states are observed slightly above EF with O2pz character depending on the doping and annealing conditions. An observed admixture of Cu 3d3z−r states to the predominant 3dx hole states at EF of a few percent did not significantly exceed the expermental error limits.KeywordsApical OxygenHubbard BandOrbital CharacterValence Band StateLower Hubbard BandThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.