  We develop a first-principles approach based on many-body perturbation theory
to investigate the effects of the interaction between electrons and carrier
plasmons on the electronic properties of highly-doped semiconductors and
oxides. Through the evaluation of the electron self-energy, we account
simultaneously for electron-plasmon and electron-phonon coupling in theoretical
calculations of angle-resolved photoemission spectra, electron linewidths, and
relaxation times. We apply this methodology to electron-doped anatase TiO2 as
an illustrative example. The simulated spectra indicate that electron-plasmon
coupling in TiO2 underpins the formation of satellites at energies comparable
to those of polaronic spectral features. At variance with phonons, however, the
energy of plasmons and their spectral fingerprints depends strongly on the
carrier concentration, revealing a complex interplay between plasmon and phonon
satellites. The electron-plasmon interaction accounts for approximately 40% of
the total electron-boson interaction strength and it is key to improve the
agreement with measured quasiparticle spectra.
