Electron-boson interactions are fundamental to a thorough understanding of various exotic properties emerging in many-body physics. The characteristics of electron-phonon/-magnon interactions in photoemission spectra have been thoroughly investigated, while less is known about the interaction between electrons and plasmons. In the 1960s, Lundgvist theoretically predicted a new composite particle, the plasmaron, caused by the strong coupling between holes and plasmons, which has extended an important research branch of complex many-body theory in condensed matter physics. However, the photoemission spectroscopic probing of conventional plasmaron or plasmonic-polaron replica located at high binding energy (～10 eV) was hindered by the relatively poor momentum resolution and possible mixup of weak plasmonic satellites and strong quasiparticle peaks.
Collaborating with Prof. Gang Li at ShanghaiTech University, Prof. Dawei Shen and Zhengtai Liu’s group at SIMIT have presented direct evidence of a low-energy polaron in the electronic structure of a semi-metallic iridium oxide SrIrO3, and realized the energy fine-tuning of such polaron using the combined oxide molecular beam epitaxy (OMBE) and angle-resolved photoelectron spectroscopy (ARPES) and first-principles calculations. The paper tilted as “Electron-plasmon interaction induced plasmonic-polaron band replication in epitaxial perovskite SrIrO3 films” has been published in Science Bulletin, 2021, 66(5):433-440.
In this work, they successfully synthesized high quality perovskite-type SrIrO3 films, and prepared a series of epitaxial SrIrO3 films of varying thicknesses by precisely controlling the growth time and rate. By utilizing integrated in situ ARPES, they first discovered the long-sought pure electron-plasmon coupling-induced low-lying plasmonic-polaron replica bands and confirmed the existence of volume plasmaron, as shown in Figure 1, which is important to obtain a complete understanding of the quasiparticle dynamics in semimetallic iridates. Besides, the researchers could adjust the carrier concentration by charge doping, and realized the effective manipulation of the polaron frequency (energy) in SrIrO3 films. These findings may provide new pathways toward plasmon-assisted bandgap tuning and the manipulation of plasmon polaritons, with potential implications for photonics and plasmonics.