Orientation of the O2p holes in Bi2Sr2Ca1 Cu2O8

Unoccupied O 2p states are observed in Bi2Sr2Ca1 Cu2O8 near the Fermi level. They show up as a spike in the O 1s absorption edge at threshold (h=528.2 eV). The orientation of these O 2p states is determined via optical selection rules from the polarization dependence of the absorption using single crystals. The O 2p holes are found to have at least 95% px,y character with x, y in the superconducting a-b plane. © 1988 The American Physical Society.