SPIN-RESOLVED PHOTOEMISSION ANTI-FERROMAGNETS - DIRECT OBSERVATION OFZHANG-RICE SINGLETS IN CUO

We demonstrate that it is possible to obtain spin-resolved valence ban d spectra with a very high degree of spin polarization from antiferrom agnetic transition metal materials if the excitation light is circular ly polarized and has an energy close to the cation 2p(3/2) (L(3)) whit e 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 vale nce band is of pure singlet character, which provides strong support f or the existence and stability of Zhang-Rice singlets in high-T-c supe rconductors.