Rare-earth-Cu interaction in high-temperature superconductors

In high-temperature superconductors two-dimensional CuO2-planes are separated by metal-oxide layers. These supply charge and separate the layers. How they influence the electronic structure and whether they couple the CuO2 layers is unclear. Using resonant photoemission we demonstrate a new technique to study such coupling. This is done by measuring the resonance of Cu-states across the rare-earth 4d level. Using Bi2Sr2(Ca,Nd)Cu2O8 as an example we show that there is a significant coupling between electronic states on Nd and Cu. (orig.)