Electron correlations in YBCO thin films using Auger, autoionization and electron energy loss spectroscopy

Abstract

The strong electron correlations among Cu 3d electrons in the Cu - O plane of YBCO have been studied using Cu Auger spectra. The possible presence of valence band (Cu 3d) partially filled states in YBCO is investigated by valence band spectroscopies - autoionization and electron energy loss spectroscopy (EELS) in reflection mode. Coulomb correlations are found to be larger than the one-electron band width . There occurs an autoionization feature at 63 eV in the low-electron-energy excited Auger spectra which is slightly higher than Cu . Further EELS exhibits a feature at 12.5 eV which can be assigned to Cu transitions. Thus autoionization and EELS together give evidence of the presence of partially filled Cu 3d states in the valence band of the YBCO superconductor. Thus Auger spectroscopy, along with autoionization and EELS, consistently proves the presence of strong electron correlations among Cu 3d electrons in the YBCO superconductor.