Evidence for a large magnetic heat current in insulating layered cuprates

The in-plane thermal conductivity k of the two-dimensional antiferromagnetic monolayer cuprate ${\mathrm{Sr}}_2{\mathrm{CuO}}_2{\mathrm{Cl}}_2$ is studied. Analysis of the unusual temperature dependence of k reveals that at low temperatures the heat is carried by phonons, whereas at high temperatures magnetic excitations contribute significantly. A comparison with other insulating layered cuprates suggests that a large magnetic contribution to the thermal conductivity is an intrinsic property of these materials.