A photoemission study (XPS and UPS) of the superconductor ErBa2Cu4O8 and comparison with YBa2Cu3O7-?(??0,1)

Abstract

Core level and valence band photoemission spectra of the “124” superconductor ErBa2Cu4O8 are investigated using MgKα, HeI, and HeII radiation and compared with photoemission spectra of orthorhombic YBa2Cu3O7 and tetragonal YBa2Cu3O6.2 samples. It is found that the Cu 2p3/2 core level and the UPS valence band spectra of ErBa2Cu4O8 and YBa2Cu3O7 are very similar but differ significantly from those of YBa2Cu3O6.2. From the resemblance between the ErBa2Cu4O8 and YBa2Cu3O7 spectra it follows that the electronic structures of these two compounds are closely related in spite of an additional CuO chain in the “124” phase. The differences between the YBa2Cu3O6.2 spectra and the other spectra are explained by the the presence of monovalent copper at the crystallographic Cu(1) sites. The Cu 2p3/2 lineshapes of the here studied superconductors and some CuII compounds are discussed.