Electron-boson interaction is fundamental to a thorough understanding of various exotic properties emerging in many-body physics. In photoemission spectroscopy, photoelectron emission due to photon absorption 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 study electron-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 is extremely challenging. Here by utilizing integrated oxide molecular-beam epitaxy and angle-resolved photoemission spectroscopy, we discover the long sought-after pure electron-plasmon coupling-induced low-lying plasmonic-polaron replica bands in epitaxial semimetallic SrIrO₃ films, in which the characteristic low carrier concentration and narrow bandwidth combine to provide a unique platform where the electron-plasmon interaction can be investigated kinematically in photoemission spectroscopy. This finding enriches the forms of electron band normalization on collective modes in solids and demonstrates that, to obtain a complete understanding of the quasiparticle dynamics in 5d electron systems, the electron-plasmon interaction should be considered on equal footing with the acknowledged electron-electron interaction and spin-orbit coupling.

电子-玻色子相互作用是透彻理解多体物理学中出现的各种奇异特性的基础。在光电子能谱中，光子吸收引起的光电子发射会在固体中引发多种集体激发，包括声子、磁振子、电子-空穴对和等离子体激元的出现，这自然为研究电子-玻色子耦合提供了可靠的途径。虽然在这种最先进的技术中电子-声子/磁振子相互作用的指纹已经得到很好的研究，但对电子-等离子体耦合知之甚少，而直接观察仅由于电子-等离子体相互作用而导致的带重整化是极具挑战性。在这里，通过利用集成氧化物分子束外延和角分辨光电子能谱，₃种薄膜，其中特有的低载流子浓度和窄带宽相结合，提供了一个独特的平台，可以在光电子能谱中以运动学方式研究电子等离子体相互作用。这一发现丰富了固体中集体模式电子能带归一化的形式，并表明，为了获得对 5 d电子系统中准粒子动力学的完整理解，电子 - 等离子体相互作用应与公认的电子 - 电子处于同等地位相互作用和自旋轨道耦合。