X-ray photoelectron studies of high-temperature superconductors: evidence for the importance of alkaline earth metals

Abstract

All high-temperature superconducting ceramics so far studied contain alkaline-earth ions, and in all cases core-level X-ray photoelectron spectroscopy shows an anomalous low-binding energy peak from these ions. We argue that this may point to electron-rick alkaline earth layers. These should be highly polarisable, allowing them to facilitate superconductivity by screening the repulsion between electrons and/or holes in the CuO layers.