Scaling behavior and giant field-enhancement of the thermal conductivity in the honeycomb antiferromagnet BaCo2(AsO4)2

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 $α$-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 $κ_{xx}$ in an in-plane magnetic field ${\bf H}$. Just above the Néel temperature $T_{\rm N}$, a field of 13 T increases $κ_{xx}$ by a factor $\sim 211$, much larger than reported previously in any magnetic insulator. Interestingly, $κ_{xx}(H,T)$ exhibits a scaling behavior in the entire magnetically disordered region that surrounds the ordered zigzag state. The ratio $Δκ_{xx}(H,T)/κ_{xx}(13,T)$, measured throughout the disordered region, collapses to a one-parameter scaling function ${\rm exp}(-1/gx)$ (where $x = μ_{\rm B}B/k_{\rm B}T$ and $g$ is a constant).