Regensburg 2025 – wissenschaftliches Programm

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SYIS: Symposium Progress and Challenges in Modelling Electron-Phonon Interaction in Solids

SYIS 1: Progress and Challenges in Modelling Electron-Phonon Interaction in Solids

SYIS 1.3: Hauptvortrag

Dienstag, 18. März 2025, 10:30–11:00, H1

Polarons and exciton polarons from first principles — •Feliciano Giustino — The University of Texas at Austin

Polarons are quasiparticles formed when a charge carrier interacts with lattice vibrations. In materials with strong electron-phonon couplings, this phenomenon results in self-trapped polarons. Similarly, excitons, which are composite quasiparticles formed by the binding of an electron and a hole, can polarize the surrounding crystal lattice through spatial fluctuations in their charge density. This polarization, in turn, can promote the spatial localization of the exciton, leading to the formation of exciton polarons or even self-trapped excitons in the presence of strong exciton-phonon couplings. First-principles calculations of these effects are challenging because they require large supercells potentially involving hundreds or thousands of atoms. In this talk, I will discuss recent methodological developments that combine density-functional perturbation theory and the Bethe-Salpeter approach to compute polarons and exciton polarons from first principles. The main advantage of the present approach is that it does not require supercells, and all necessary information is generated via calculations in the crystal unit cell. To illustrate these developments, I will report on two recent applications: (i) the discovery of topological polarons in halide perovskites, wherein the distortion of the atomic lattice describes a vector field with definite topological invariants; and (ii) the discovery of large polarons and exciton polarons in rutile and anatase titanium dioxide, which provide a natural explanation for why anatase exhibits diffusive carrier transport while rutile supports thermally-activated transport.

Keywords: Polarons; Exciton polarons; Exciton-phonon couplings; Halide perovskites; Titanium dioxide