Interpretation of doping phenomena in high-Tc superconductors

On the basis of an indirect-exchange pairing mechanism of superconducitivity, a consistent interpretation of doping phenomena in both hole-doped as well as electron-doped high-Tc superconductors is presented. It is argued that in all these materials the unifying feature is the existence of a correlated narrow band of electron states formed due to doping. Numerous experimental evidences for the occurrence of such a band (reflectivity, thermoelectric power, electrical resisitivity, X-ray absorption, point-contact tunneling etc.) now exist. Assuming the existence of such a band it was earlier shown that the indirect-exchange (superexchange) coupling between electrons in this via closed oxygen anions is attractive in the s-wave channel and leads to high-Tc superconductivity. Within the frame-work of this pairing mechanism, recent doping experiments (for both types of doping) can be given a unified interpreation. In addition, definitive predictions of the doping conditions under which critical temperatures are expected to enhance, are made. (author). 48 refs