The Electronic States Formed by Doping La2CuO4 Giving High Tc Superconductivity Determined by Cu L3 Edge X-Ray Absorption Spectroscopy

Abstract

The results of the recent works on the L3-edge x-ray absorption spectra (XAS) of high Tc superconductors are discussed and a detailed comparison between 2p-XPS and 2p-XAS of La2CuO4 is reported. La2Cu04 was found to be a correlated covalent oxide and its electronic structure exhibits the interatomic intermediate valent state described by mixing between the many body configurations 3d9 and 3d10 L where one holefluctuatesbetween the oxygen derived band, ligand hole L, and Cu 3d orbital d. The ligand hole binding energy εL has been measured in CuO, La2CuO4 and YBa2Cu3O6.5 Doping La2CuO4 by Sr gives the electronic states at the Fermi level 3d9 L * or d L* where two holes are in the same CuO4 site. These states are detected by L3-edge XAS by a new peak at 932.2 eV due to transitions from the initial state 3d9 L* to the final state 2p3d10L.*The energy εL* to excite a second ligand hole L* is found by measuring the energy separation between the cL XAS final state ( c is the 2p core hole) and the cL 2 XPS final state induced by doping. The superconducting state is assigned to pairing of 3d9 L* states.KeywordsEnergy SeparationSchematic PictureCore HoleCrystal Field SplittingMetal OrbitalThese 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.