Electronic structure of YBa2Cu3Ox and YBa2Cu4O8 studied by soft-x-ray absorption and emission spectroscopies

The electronic structure of YBa2CU3O6.02, YBa2Cu3O6.94 and YBa2Cu4O8 has be en studied by using soft-xray absorption and emission spectroscopies. The u noccupied and occupied states are reflected by O 1s is absorption and O K a lpha emission spectra. An absorption prepeak appearing at 528.5 eV in the O 1s absorption spectra of YBa2Cu3O6.94 and YBa2Cu4O8 indicates the transfer ring of spectral weight from stares in the upper Hubbard band to the upper edge of the valence band. The absorption-emission spectra of YBa2Cu3O6.94 a naYBa(2)Cu(4)O(8) show the unbroken density of states crossing the Fermi le vel reflecting the metallic character of these compounds. No significant sh ape changes are observed in the resonant excited O K alpha spectra of YBa2C u3O6.94 and YBa2CU4O8. However, some small variations in spectral profile a re attributed to the changes in the relative number of excited oxygen atoms from inequivalent sites. Strong spectral changes are observed in the reson ant O K alpha spectra of YBa2Cu3O6.94 which is attributed to the strong cov alent chemical bonds between inequivalent oxygen atoms and different charge -state copper atoms. The analysis of x-ray absorption and resonant x-ray em ission spectra provides the character of unoccupied states of YBa2CU3O6.02, YBa2CU3O6.94, and YBa2Cu4O8. The experimental findings suggest an existenc e of an appreciable amount of doping-induced holes at O(1) and O(4) sites a nd an importance of O(1)-Cu(1)-O(4) ribbons for superconducting properties of YBa2Cu3O7-delta and YBa2CU4O8-delta.