Anomalous thermal transport and violation of Wiedemann-Franz law in the critical regime of a charge density wave transition

TL;DR

This study investigates thermal transport in ErTe$_3$, revealing a violation of the Wiedemann-Franz law near the charge density wave transition, indicating a strongly coupled electron-phonon critical state.

Contribution

It provides experimental evidence of anomalous thermal transport and Wiedemann-Franz law violation in a CDW material's critical regime, highlighting a coupled electron-phonon state.

Findings

Thermal conductivity sharply decreases at the CDW transition.

Wiedemann-Franz law holds outside the critical regime.

Violation of Wiedemann-Franz law occurs in the critical regime.

Abstract

ErTe$_3$ is studied as a model system to explore thermal transport in a layered charge density wave (CDW) material. We present data from thermal diffusivity, resistivity, and specific heat measurements: There is a sharp decrease in thermal conductivity both parallel and perpendicular to the primary CDW at the CDW transition temperature. At the same time, the resistivity changes more gradually. Correspondingly, while well above and below $T_c$, a consistent description of the thermal transport applies with essentially independent electron and phonon contributions (estimated using the Wiedemann Franz law), in the critical regime no such description is possible; the observed behavior corresponds to a strongly coupled electron-phonon critical `soup.'