The x-ray-photoelectron-spectroscopy of several layered oxides provide no Cu(2p) evidence for Cu(III), but exhibit an extra O(1s) peak where direct contact between oxygen atoms occurs within the Cu(1) planes of the ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ structure. The extra peak has a binding energy typical of that for a peroxide ion (${\mathrm{O}}_2$${)}^2$. This observation, in conformity with earlier prediction, provides compelling evidence for holes in the O 2p bands of the high-$T_c$ copper-oxide superconductors.

• Received 2 May 1988

DOI:https://doi.org/10.1103/PhysRevB.38.5091