Evolution of a Polaron Band through the Phase Diagram ofNd2xCexCuO4y

Abstract
The evolution with doping and temperature of the polaronic absorption in a family of high- Tc superconductors is followed across the whole phase diagram. The polaron band softens with increasing doping, is still present in the superconducting phase, and vanishes in the overdoped metallic phase. These results point toward the existence of polaron aggregates at low temperature and provide an experimental ground for the increasing number of theoretical descriptions of many-polaron systems.