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

The layered honeycomb material BaCo2(AsO₄)₂ is of topical interest because its magnetic state is related to that of the Kitaev magnet α-RuCl₃. 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 H. Just above the Néel temperature T_N, a field of 13 T increases κ_xx by a factor of ∼211, which is very large compared to other magnetic insulators. 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 exp(−1/gx) (where x=μ_BB/k_BT and g is a constant).