Field-dependent heat transport in the Kondo insulator SmB6 : phonons scattered by magnetic impurities

TL;DR

This study measures the thermal conductivity of SmB6 at very low temperatures and high magnetic fields, revealing phonon-dominated heat transport with impurity scattering and no evidence of fermionic carriers.

Contribution

It provides detailed low-temperature, high-field thermal conductivity data for SmB6, highlighting the role of magnetic impurity scattering and anisotropic phonon transport.

Findings

Residual linear thermal conductivity is zero, indicating no fermionic heat carriers.

Thermal conductivity increases with magnetic field, showing anisotropic behavior.

Heat transport is mainly via phonons scattered by magnetic impurities.

Abstract

The thermal conductivity $\kappa$ of the Kondo insulator SmB$_6$ was measured at low temperature, down to 70 mK, in magnetic fields up to 15 T, on single crystals grown using both the floating-zone and the flux methods. The residual linear term $\kappa_0/T$ at $T \to 0$ is found to be zero in all samples, for all magnetic fields, in agreement with previous studies. There is therefore no clear evidence of fermionic heat carriers. In contrast to some prior data, we observe a large enhancement of $\kappa(T)$ with increasing field. The effect of field is anisotropic, depending on the relative orientation of field and heat current (parallel or perpendicular), and with respect to the cubic crystal structure. We interpret our data in terms of heat transport predominantly by phonons, which are scattered by magnetic impurities.