Empty states near the Fermi level in Bi2Sr2CaCu2O8

Abstract

Unoccupied states are seen at the Fermi level in ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_8$ 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 $E_F$+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).