X-RAY-EMISSION FROM HIGH-TC SUPERCONDUCTORS - ROLE OF APICAL OXYGEN

X-ray emission can serve as a local probe of the Cu 3d or O 2p states. The O K emission integrates information from all oxygen atoms whether directly coordinated to copper sites or not. The O K emission is clearly band-like. The Cu L3 spectrum provides more direct information on the Cu - O unit. Because the initial state is a core hole emphasis is placed on correlation effects the presence of which infirm local density approximation predictions. We observe, however, small but significant changes in the width and shape of the Cu L3 emission according to the compound which we relate to structure and variations in Cu - O bonding.