https://doi.org/10.1016/j.scib.2020.10.003

Electron-boson interaction is fundamental to a thorough understanding of various exotic propertiesemerging in many-body physics. In photoemission spectroscopy, photoelectron emission due to photonabsorption would trigger diverse collective excitations in solids, including the emergence of phonons,magnons, electron-hole pairs, and plasmons, which naturally provides a reliable pathway to studyelectron-boson couplings. While fingerprints of electron–phonon/-magnon interactions in this state-of-the-art technique have been well investigated, much less is known about electron-plasmon coupling,and direct observation of the band renormalization solely due to electron-plasmon interactions isextremely challenging. Here by utilizing integrated oxide molecular-beam epitaxy and angle-resolvedphotoemission spectroscopy, we discover the long sought-after pure electron-plasmon coupling-induced low-lying plasmonic-polaron replica bands in epitaxial semimetallic SrIrO3films, in which thecharacteristic low carrier concentration and narrow bandwidth combine to provide a unique platformwhere the electron-plasmon interaction can be investigated kinematically in photoemission spec-troscopy. This finding enriches the forms of electron band normalization on collective modes in solidsand demonstrates that, to obtain a complete understanding of the quasiparticle dynamics in 5delectronsystems, the electron-plasmon interaction should be considered on equal footing with the acknowledgedelectron–electron interaction and spin–orbit coupling.