# Finite-temperature violation of the anomalous transverse Wiedemann-Franz law

## TL;DR

This study investigates the anomalous transverse transport in Mn$_{3}$Ge across a wide temperature range, revealing a finite-temperature violation of the Wiedemann-Franz law caused by Berry curvature effects, supported by theoretical calculations.

## Contribution

It demonstrates that the anomalous Lorenz ratio deviates from the Sommerfeld value at higher temperatures due to Berry curvature mismatch, providing new insights into topological transport phenomena.

## Key findings

- Anomalous Lorenz ratio remains near the Sommerfeld value up to 100 K.
- Finite-temperature violation caused by Berry curvature mismatch, not inelastic scattering.
- Experimental verification of the Bridgman relation supports the results.

## Abstract

The Wiedemann-Franz (WF) law links the ratio of electronic charge and heat conductivity to fundamental constants. It has been tested in numerous solids, but the extent of its relevance to the anomalous transverse transport, which represents the topological nature of the wave function, remains an open question. Here we present a study of anomalous transverse response in the noncollinear antiferromagnet Mn$_{3}$Ge extended from room temperature down to sub-Kelvin temperature and find that the anomalous Lorenz ratio remains close to the Sommerfeld value up to 100 K, but not above. The finite-temperature violation of the WF correlation is caused by a mismatch between the thermal and electrical summations of the Berry curvature, rather than the inelastic scattering as observed in ordinary metals. This interpretation is backed by our theoretical calculations, which reveals a competition between the temperature and the Berry curvature distribution. The accuracy of the experiment is supported by the verification of the Bridgman relation between the anomalous Ettingshausen and Nernst effects. Our results identify the anomalous Lorenz ratio as an extremely sensitive probe of Berry spectrum near the chemical potential.