Empty states near the Fermi level in Bi2Sr2CaCu2O8

Unoccupied states are seen at the Fermi level in Bi2Sr2CaCu2O8 by use of inverse photoemission. They have partial oxygen 2p character, as evidenced by a resonance at the O 2s core-level threshold and by the similarity between the inverse photoemission spectrum and the O 1s absorption edge. These states are likely to be related to the hole states introduced by doping of oxide superconductors. A peak at EF+2.9 eV can be assigned to the unoccupied Cu 3d states (if they are localized) or to the Bi 6p states (for delocalized Cu 3d states). © 1989 The American Physical Society.