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

TL;DR

This study reveals a giant, field-dependent enhancement of thermal conductivity in the honeycomb antiferromagnet BaCo2(AsO4)2, with a unique scaling behavior in the magnetically disordered regime, indicating strong magnetic-phonon interactions.

Contribution

It demonstrates an unprecedented large increase in thermal conductivity under magnetic field and uncovers a universal scaling law in the disordered magnetic state.

Findings

Thermal conductivity increases by a factor of ~211 at 13 T near T_N.

Thermal conductivity exhibits a one-parameter scaling behavior in the disordered regime.

The scaling function is exp(-1/gx), linking magnetic field, temperature, and magnetic excitations.

Abstract

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).