Magnon Heat Transport in doped $\mathrm{L}{\mathrm{a}}_2\mathrm{C}\mathrm{u}{\mathrm{O}}_4$

We present results of the thermal conductivity of $\mathrm{L}{\mathrm{a}}_2\mathrm{C}\mathrm{u}{\mathrm{O}}_4$ and $\rm La_{1.8}Eu_{0.2}CuO_4$ single-crystals which represent model systems for the two-dimensional spin-1/2 Heisenberg antiferromagnet on a square lattice. We find large anisotropies of the thermal conductivity, which are explained in terms of two-dimensional heat conduction by magnons within the CuO${}_2$ planes. Non-magnetic Zn substituted for Cu gradually suppresses this magnon thermal conductivity ${\kappa }_{\mathrm{m}\mathrm{a}\mathrm{g}}$. A semiclassical analysis of ${\kappa }_{\mathrm{m}\mathrm{a}\mathrm{g}}$ is shown to yield a magnon mean free path which scales linearly with the reciprocal concentration of Zn-ions.