Thermal conductivity of the Kondo semiconductor CeRu${}_4$Sn${}_6$

We report measurements of the thermal conductivity $\kappa$ on single crystalline CeRu${}_4$Sn${}_6$ in the temperature range between 80mK and 80K, along the main crystallographic directions. $\kappa$ is phonon-dominated in the whole temperature range and is found to be essentially isotropic. At low temperatures the data are well approximated by $\kappa \propto T^2$, which is attributed to a predominant scattering of phonons on electrons. We describe the data with a Callaway fit in the whole temperature range giving good agreement at low and high temperatures.