First-principles calculations of polarons in real materials
Carla Verdi, Faculty of Physics, University of Vienna
Abstract. — Polarons are quasiparticles formed by electrons ‘dressed’ by a phonon cloud and represent a paradigmatic example of an emergent state in condensed matter. The presence of polarons can strongly influence the fundamental characteristics and functionalities of the host materials. Despite the broad scientific and technological interest in polarons, their properties are poorly understood. In this talk, I will present our recent work aimed at describing polarons from first principles in real materials.
In the first part, I will focus on doped oxides, where the polaronic nature of the charge carriers can be revealed by angle-resolved photoemission spectroscopy (ARPES) through the observation of satellites in the photoemission spectra. I will outline our framework to calculate ARPES spectra from first principles by combining ab initio calculations of the electron-phonon coupling with the cumulant expansion method . A similar framework can be applied to other forms of electron-boson coupling, such as the coupling of electrons to low-energy carrier plasmons . I will show applications to anatase TiO2 and the ferromagnetic semiconductor EuO, comparing our results to experiments and investigating the polaronic features and their weakening with increasing doping concentration.
In the second part of the talk, I will present a new approach to study polarons from first principles in semiconductors and insulators [3,4]. This approach can seamlessly describe large and small polarons, without using supercells, and enables systematic calculations of polaron energies and their localized wavefunctions. The theory can be also used to analyze the dominant mechanisms of electron-phonon coupling leading to the polaronic self-trapping, as showcased for the electron and hole polarons in LiF and Li2O2.
 C. Verdi, F. Caruso, and F. Giustino, Nat. Commun. 8, 15769 (2017).
 J. M. Riley et al., Nat. Commun. 9, 2305 (2018).
 W. H. Sio, C. Verdi, S. Poncé, and F. Giustino, Phys. Rev. Lett. 122, 246403 (2019).
 W. H. Sio, C. Verdi, S. Poncé, and F. Giustino, Phys. Rev. B 99, 235139 (2019).
Host: Walter Lambrecht