Thermal conductivity of doped $\rm\bf La_2CuO_4$ as an example for heat transport by optical phonons in complex materials

TL;DR

This study explores the unusual temperature dependence of phonon thermal conductivity in doped La2CuO4, suggesting optical phonons significantly contribute to heat transport in complex materials.

Contribution

It provides experimental evidence that optical phonons can dominate heat transport, challenging the conventional focus on acoustic phonons in complex materials.

Findings

Thermal conductivity deviates from expected T^{-1} behavior at high temperatures.

Optical phonons are proposed as a key heat transport mechanism.

Unusual temperature dependence observed in doped La2CuO4.

Abstract

We investigate the phonon thermal conductivity $\kappa_{\mathrm{ph}}$ of doped $\rm La_2CuO_4$ based on out-of-plane thermal conductivity measurements. When room temperature is approached the temperature dependence of $\kappa_{\mathrm{ph}}$ strongly deviates from the $T^{-1}$-decrease which is usually expected for heat transport by acoustic phonons. Instead, $\kappa_{\mathrm{ph}}$ decreases much weaker or even increases with rising temperature. Simple arguments suggest that such unusual temperature dependencies of $\kappa_{\mathrm{ph}}$ are caused by heat transport via dispersive optical phonons.