Diffusive energy transport in theS=1Haldane chain compoundAgVP2S6

We present the results of measurements of the thermal conductivity $\kappa$ of the spin $S=1\mathrm{}$ chain compound ${\mathrm{AgVP}}_2{\mathrm{S}}_6$ in the temperature range between 2 and 300 K and with the heat flow directed either along or perpendicular to the chain direction. The analysis of the anisotropy of the heat transport allowed for the identification of a small but non-negligible magnon contribution ${\kappa }_m$ along the chains, superimposed on the dominant phonon contribution ${\kappa }_{\mathrm{ph}}.$ At temperatures above about 100 K the energy diffusion constant $D_E\mathrm{}\left(T\right),$ calculated from the ${\kappa }_m\mathrm{}\left(T\right)\mathrm{}$ data, exhibits similar features as the spin diffusion constant $D_S\mathrm{}\left(T\right),$ previously measured by NMR. In this regime, the behavior of both transport parameters is consistent with a diffusion process that is caused by interactions inherent to one-dimensional $S=1\mathrm{}$ spin systems.