# Predicting charge transport in the presence of polarons: The beyond-quasiparticle regime in SrTiO$_{\mathrm{3}}$

## TL;DR

This paper introduces a first-principles method to accurately predict charge transport in SrTiO$_{3}$ with strong electron-phonon interactions, revealing a transition from quasiparticle to incoherent transport regimes with temperature.

## Contribution

It develops a cumulant diagram-resummation technique to model strong electron-phonon interactions and predicts charge transport beyond the quasiparticle approximation in polar materials.

## Key findings

- Accurately predicts electron mobility in SrTiO$_{3}$ between 150-300 K.
- Identifies a transition from band-like to incoherent charge transport with increasing temperature.
- Provides a broadly applicable method for materials with strong electron-phonon interactions.

## Abstract

In materials with strong electron-phonon ($e$-ph) interactions, the electrons carry a phonon cloud during their motion, forming quasiparticles known as polarons. Predicting charge transport and its temperature dependence in the polaron regime remains an open challenge. Here, we present first-principles calculations of charge transport in a prototypical material with large polarons, SrTiO$_{3}$. Using a cumulant diagram-resummation technique that can capture the strong $e$-ph interactions, our calculations can accurately predict the experimental electron mobility in SrTiO$_{3}$ between 150$-$300 K. They further reveal that for increasing temperature the charge transport mechanism transitions from band-like conduction, in which the scattering of renormalized quasiparticles is dominant, to a beyond-quasiparticle transport regime governed by incoherent contributions due to the interactions between the electrons and their phonon cloud. Our work reveals long-sought microscopic details of charge transport in SrTiO$_{3}$, and provides a broadly applicable method for predicting charge transport in materials with strong $e$-ph interactions and polarons.