The Lorenz number in CeCoIn$_5$ inferred from the thermal and charge Hall currents

TL;DR

This paper investigates the thermal and charge Hall effects in CeCoIn$_5$, revealing a charge-neutral thermal component linked to spin excitations and demonstrating how high magnetic fields influence electron scattering and transport properties.

Contribution

It introduces a method to separate electronic and non-electronic thermal conductivity in CeCoIn$_5$ using Hall measurements, uncovering spin excitations' role in thermal transport.

Findings

Identification of a charge-neutral, field-dependent thermal conductivity component.

Evidence that spin excitations dominate low-temperature scattering.

Discovery of a scaling relation between magnetoresistance, thermal conductivity, and Hall conductivity.

Abstract

The thermal Hall conductivity $\kappa_{xy}$ and Hall conductivity $\sigma_{xy}$ in CeCoIn$_5$ are used to determine the Lorenz number ${\cal L}_H$ at low temperature $T$. This enables the separation of the observed thermal conductivity into its electronic and non-electronic parts. We uncover evidence for a charge-neutral, field-dependent thermal conductivity, which we identify with spin excitations. At low $T$, these excitations dominate the scattering of charge carriers. We show that suppression of the spin excitations in high fields leads to a steep enhancement of the electron mean-free-path, which leads to an interesting scaling relation between the magnetoresistance, thermal conductivity and $\sigma_{xy}$.