# Ultrafast acoustic phonon scattering in CH$_3$NH$_3$PbI$_3$ revealed by femtosecond four-wave mixing

## TL;DR

This study investigates carrier scattering mechanisms in CH$_3$NH$_3$PbI$_3$ using femtosecond four-wave mixing, revealing ionized impurity effects at low temperatures and strong electron-phonon interactions at higher temperatures, with theoretical insights into spin-orbit coupling effects.

## Contribution

It provides the first detailed experimental and theoretical analysis of ultrafast acoustic phonon scattering in CH$_3$NH$_3$PbI$_3$, highlighting the role of spin-orbit coupling and Rashba effects.

## Key findings

- Ionized impurities limit dephasing below 30 K
- Electron-phonon scattering dominates at 100 K with 125 fs timescale
- Spin-orbit coupling enhances acoustic phonon scattering rate

## Abstract

Carrier scattering processes are studied in CH$_3$NH$_3$PbI$_3$ using temperature-dependent four-wave mixing experiments. Our results indicate that scattering by ionized impurities limits the interband dephasing time (T$_2$) below 30~K, with strong electron-phonon scattering dominating at higher temperatures (with a timescale of 125 fs at 100 K). Our theoretical simulations provide quantitative agreement with the measured carrier scattering rate and show that the rate of acoustic phonon scattering is enhanced by strong spin-orbit coupling, which modifies the band-edge density of states. The Rashba coefficient extracted from fitting the experimental results ($\gamma_c=2$ eV angstrom) is in agreement with calculations of the surface Rashba effect and recent experiments using the photogalvanic effect on thin films.