# Magnon-polaron transport in magnetic insulators

## TL;DR

This paper develops a theoretical framework for magnon-polaron transport in magnetic insulators, explaining experimental anomalies and predicting new effects in spin and heat transport due to strong magnetoelastic coupling.

## Contribution

It introduces a Boltzmann transport theory for magnon polarons and explains experimental observations, predicting novel transport phenomena in magnetic insulators.

## Key findings

- Magnon-polaron formation causes anomalous magnetic field and temperature dependence in spin Seebeck effect.
- Experimental data on yttrium iron garnet can be explained by better acoustic quality than magnetic quality.
- Predicted similar anomalies in spin and heat conductivity and non-local spin transport experiments.

## Abstract

We theoretically study the effects of strong magnetoelastic coupling on the transport properties of magnetic insulators. We develop a Boltzmann transport theory for the mixed magnon-phonon modes (magnon polarons) and determine transport coefficients and spin diffusion length. Magnon-polaron formation causes anomalous features in the magnetic field and temperature dependence of the spin Seebeck effect when the disorder scattering in the magnetic and elastic subsystems is sufficiently different. Experimental data by Kikkawa et al. [PRL 117, 207203 (2016)] on yttrium iron garnet films can be explained by an acoustic quality that is much better than the magnetic quality of the material. We predict similar anomalous features in the spin and heat conductivity and non-local spin transport experiments.