Magnetic thermal conductivity far above the N\'eel temperatures in the Kitaev-magnet candidate $\alpha$-RuCl$_{3}$

Understand

We have investigated the longitudinal thermal conductivity of $\alpha$-RuCl$_{3}$, the magnetic state of which is considered to be proximate to a Kitaev honeycomb model, along with the spin susceptibility and magnetic specific heat.

• We found that the temperature dependence of the thermal conductivity exhibits an additional peak around 100 K, which is well above the phonon peak temperature ($\sim$ 50 K).
• The higher-temperature peak position is comparable to the temperature scale of the Kitaev couplings rather than the N\'eel temperatures below 15 K.
• The additional heat conduction was observed for all five samples used in this study, and was found to be rather immune to a structural phase transition of $\alpha$-RuCl$_{3}$, which suggests its different origin from phonons.