Fig. 3

Doping-dependent plasmonic polarons. a–d Evolution of the measured spectral function of Eu_1−xGd _x O with increasing charge carrier doping, showing not only a strong increase in band filling of the quasiparticle band, but also a substantial evolution of the satellite peak structure. The insets show Fermi surface contours (hν = 137 eV), indicating the increasing doping. While replica bands can still be observed to high doping, as clearly evident as peak-dip-hump structures in measured EDCs (e), these show a strong broadening and blue-shift relative to the quasiparticle peak with increasing doping. f–i Our ab initio calculations reproduce this general trend when both electron−phonon and electron−plasmon interactions are considered, identifying the hump feature in the higher-density samples as arising from plasmonic polarons