Anomalous thermal conductivity and magnetic torque response in the honeycomb magnet $\alpha$-RuCl$_3$

Abstract

We report on the unusual behavior of the in-plane thermal conductivity ($\kappa$) and torque ($\tau$) response in the Kitaev-Heisenberg material $\alpha$-RuCl$_3$. $\kappa$ shows a striking enhancement with linear growth beyond H = 7 T, where magnetic order disappears, while $\tau$ for both of the in-plane symmetry directions shows an anomaly at the same field. The temperature- and field-dependence of $\kappa$ are far more complex than conventional phonon and magnon contributions, and require us to invoke the presence of unconventional spin excitations whose properties are characteristic of a field-induced spin-liquid phase related to the enigmatic physics of the Kitaev model in an applied magnetic field