Heat transport by lattice and spin excitations in the spin-chain compounds ${\mathrm{SrCuO}}_2$ and ${\mathrm{Sr}}_2{\mathrm{CuO}}_3$

We present the results of measurements of the thermal conductivity of the quasi-one-dimensional $S=1/2\mathrm{}$ spin-chain compound ${\mathrm{SrCuO}}_2$ in the temperature range between 0.4 and 300 K along the directions parallel and perpendicular to the chains. An anomalously enhanced thermal conductivity is observed along the chains above about 40 K. The analysis of the present data and a comparison with analogous recent results for ${\mathrm{Sr}}_2{\mathrm{CuO}}_3$ and other similar materials demonstrates that this behavior is generic for cuprates with copper-oxygen chains and strong intrachain interactions. The observed anomalies are attributed to the one-dimensional energy transport by spin excitations (spinons), limited by the interaction between spin and lattice excitations. The energy transport along the spin chains has a nondiffusive character, in agreement with theoretical predictions for integrable models.