Spin-Resolved Photoemission on Anti-Ferromagnets: Direct Observation of Zhang-Rice Singlets in CuO

Abstract

We demonstrate that it is possible to obtain spin-resolved valence band spectra with a very high degree of spin polarization from antiferromagnetic transition metal materials if the excitation light is circularly polarized and has an energy close to the cation 2p3/2 (L3) white line. We are able to unravel the different spin states in the single-particle excitation spectrum of CuO and show that the top of the valence band is of pure singlet character, which provides strong support for the existence and stability of Zhang-Rice singlets in high-Tc superconductors.