The layered honeycomb material BaCo$_2$(AsO$_4$)$_2$ (BCAO) is of topical interest because its magnetic state is related to that of the Kitaev magnet $\alpha$-RuCl$_3$. Using thermal transport to probe how magnetic excitations interact with phonons in the magnetically disordered regime, we have uncovered an unusually large enhancement of the thermal conductivity $\kappa_{ xx}$ in an in-plane magnetic field ${ \bf H}$. Just above the N\'{ e}el temperature $T_{ \rm N}$, a field of 13 T increases $\kappa_{ xx}$ by a factor $\sim 211$, much larger than reported previously in any magnetic insulator. Interestingly, $\kappa_{ xx}(H,T)$ exhibits a scaling behavior in the entire magnetically disordered region that surrounds the ordered zigzag state. The ratio $\Delta \kappa_{ xx}(H,T)/\kappa_{ xx}(13,T)$, measured throughout the disordered region, collapses to a one-parameter scaling function ${ \rm exp}(-1/gx)$ (where $x = \mu_{ \rm B}B/k_{ \rm B}T$ and $g$ is a constant).
Categories: cond-mat.str-el cond-mat.mtrl-sci