Theoretical approaches to Fr\"ohlich excitonic polarons in polar semiconductors

TL;DR

This paper reviews empirical models of Frohlich excitonic polarons in polar semiconductors, highlighting their physical properties and deviations in 3D perovskites due to electron-hole correlations.

Contribution

It provides an overview of empirical approaches with some original developments for modeling excitonic polarons, extending the LLP model to include electron-hole interactions.

Findings

Excitonic polarons characterized by effective masses and binding energies.

Significant electron-hole correlation effects in 3D perovskites.

Long-range Frohlich interaction dominates polaron properties.

Abstract

Short abstract: The paper reviews the physics of Fr\"ohlich excitonic polarons from the viewpoint of empirical approaches with some original developments. Models for excitonic polarons in ionic semiconductors in the spirit of the Lee Low and Pines (LLP) model for free polarons were initiated by Toyozawa and Hermanson and extended by Pollman and Buttner (PB). The dominant electron-hole interaction with the lattice introduced by Frohlich is represented by a long-range effective interaction with a single longitudinal optical polar mode. The properties of the excitonic polarons are characterized by various physical quantities such as effective dielectric constants, effective masses, virtual phonon populations, carrier self-energies and binding energies, and effective electron-hole interactions mediated by the lattice. In 3D perovskites, the excitonic polarons deviate from the simplified picture of weakly interacting (almost free) polarons, with sizeable effects of electron-hole correlations on all the physical properties.